Fix inferring return type of var function (#545)

I accidentally broke the detection of the return type in:

```js
var f = function(x: number): boolean {}
```

Author: arv

lib/infer/return.js

@@ -1,6 +1,6 @@
 'use strict';
 
-var finders = require('./finders'),
+var findTarget = require('./finders').findTarget,
   t = require('babel-types'),
   shouldSkipInference = require('./should_skip_inference'),
   flowDoctrine = require('../flow_doctrine');
@@ -17,8 +17,15 @@ module.exports = function () {
     if (comment.returns) {
       return comment;
     }
-    var path = finders.findTarget(comment.context.ast);
+    var path = findTarget(comment.context.ast);
     var fn = path && path.node;
+
+    // In case of `/** */ var x = function () {}` findTarget returns
+    // the declarator.
+    if (t.isVariableDeclarator(fn)) {
+      fn = fn.init;
+    }
+
     if (t.isFunction(fn) &&
       fn.returnType &&
       fn.returnType.typeAnnotation) {

test/fixture/var-function-param-return.input.js

@@ -0,0 +1,2 @@
+/** */
+var f = function(x: number): boolean {}

test/fixture/var-function-param-return.output.json

@@ -0,0 +1,61 @@
+[
+  {
+    "description": "",
+    "tags": [],
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 6
+      }
+    },
+    "context": {
+      "loc": {
+        "start": {
+          "line": 2,
+          "column": 0
+        },
+        "end": {
+          "line": 2,
+          "column": 39
+        }
+      }
+    },
+    "errors": [],
+    "name": "f",
+    "kind": "function",
+    "params": [
+      {
+        "title": "param",
+        "name": "x",
+        "lineNumber": 2,
+        "type": {
+          "type": "NameExpression",
+          "name": "number"
+        }
+      }
+    ],
+    "returns": [
+      {
+        "type": {
+          "type": "NameExpression",
+          "name": "boolean"
+        }
+      }
+    ],
+    "members": {
+      "instance": [],
+      "static": []
+    },
+    "path": [
+      {
+        "name": "f",
+        "kind": "function"
+      }
+    ],
+    "namespace": "f"
+  }
+]

test/fixture/var-function-param-return.output.md

@@ -0,0 +1,9 @@
+<!-- Generated by documentation.js. Update this documentation by updating the source code. -->
+
+# f
+
+**Parameters**
+
+-   `x` **[number](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number)** 
+
+Returns **[boolean](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean)** 

test/fixture/var-function-param-return.output.md.json

@@ -0,0 +1,101 @@
+{
+  "type": "root",
+  "children": [
+    {
+      "type": "html",
+      "value": "<!-- Generated by documentation.js. Update this documentation by updating the source code. -->"
+    },
+    {
+      "depth": 1,
+      "type": "heading",
+      "children": [
+        {
+          "type": "text",
+          "value": "f"
+        }
+      ]
+    },
+    {
+      "type": "strong",
+      "children": [
+        {
+          "type": "text",
+          "value": "Parameters"
+        }
+      ]
+    },
+    {
+      "ordered": false,
+      "type": "list",
+      "children": [
+        {
+          "type": "listItem",
+          "children": [
+            {
+              "type": "paragraph",
+              "children": [
+                {
+                  "type": "inlineCode",
+                  "value": "x"
+                },
+                {
+                  "type": "text",
+                  "value": " "
+                },
+                {
+                  "type": "strong",
+                  "children": [
+                    {
+                      "href": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number",
+                      "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number",
+                      "type": "link",
+                      "children": [
+                        {
+                          "type": "text",
+                          "value": "number"
+                        }
+                      ]
+                    }
+                  ]
+                },
+                {
+                  "type": "text",
+                  "value": " "
+                }
+              ]
+            }
+          ]
+        }
+      ]
+    },
+    {
+      "type": "paragraph",
+      "children": [
+        {
+          "type": "text",
+          "value": "Returns "
+        },
+        {
+          "type": "strong",
+          "children": [
+            {
+              "href": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean",
+              "url": "https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean",
+              "type": "link",
+              "children": [
+                {
+                  "type": "text",
+                  "value": "boolean"
+                }
+              ]
+            }
+          ]
+        },
+        {
+          "type": "text",
+          "value": " "
+        }
+      ]
+    }
+  ]
+}