docs: add syntax highlighting to sample-nodemon.md (#1982) (#2004)

[skip ci]

Co-authored-by: Chris Calo <[email protected]>

Author: remy

doc/sample-nodemon.md

@@ -2,27 +2,29 @@
 
 Here is an example (of a contrived) `nodemon.json` file:
 
-    {
-      "restartable": "rs",
-      "ignore": [
-        ".git",
-        "node_modules/**/node_modules"
-      ],
-      "verbose": true,
-      "execMap": {
-        "js": "node --harmony"
-      },
-      "events": {
-        "restart": "osascript -e 'display notification \"App restarted due to:\n'$FILENAME'\" with title \"nodemon\"'"
-      },
-      "watch": [
-        "test/fixtures/",
-        "test/samples/"
-      ],
-      "env": {
-        "NODE_ENV": "development"
-      },
-      "ext": "js,json"
-    }
+```json
+{
+  "restartable": "rs",
+  "ignore": [
+    ".git",
+    "node_modules/**/node_modules"
+  ],
+  "verbose": true,
+  "execMap": {
+    "js": "node --harmony"
+  },
+  "events": {
+    "restart": "osascript -e 'display notification \"App restarted due to:\n'$FILENAME'\" with title \"nodemon\"'"
+  },
+  "watch": [
+    "test/fixtures/",
+    "test/samples/"
+  ],
+  "env": {
+    "NODE_ENV": "development"
+  },
+  "ext": "js,json"
+}
+```
 
 Note that the `ignore` used is nodemon's default ignore rule. The complete defaults can be seen here: [defaults.js](https://github.com/remy/nodemon/blob/master/lib/config/defaults.js).