Fix linting errors

In #1277 we enabled some new eslint rules, but the branch hadn't been
freshly rebased, so a few failures snuck in. I fixed these by running

```sh
npm run lint -- --fix
```

Author: lencioni

lib/rules/boolean-prop-naming.js

@@ -47,7 +47,7 @@ module.exports = {
     const propTypeNames = config.propTypeNames || ['bool'];
 
     // Remembers all Flowtype object definitions
-    var objectTypeAnnotations = new Map();
+    const objectTypeAnnotations = new Map();
 
     /**
      * Checks if node is `propTypes` declaration

tests/lib/rules/boolean-prop-naming.js

@@ -8,12 +8,12 @@
 // Requirements
 // ------------------------------------------------------------------------------
 
-var rule = require('../../../lib/rules/boolean-prop-naming');
-var RuleTester = require('eslint').RuleTester;
+const rule = require('../../../lib/rules/boolean-prop-naming');
+const RuleTester = require('eslint').RuleTester;
 
 require('babel-eslint');
 
-var parserOptions = {
+const parserOptions = {
   ecmaVersion: 6,
   sourceType: 'module',
   ecmaFeatures: {
@@ -25,7 +25,7 @@ var parserOptions = {
 // Tests
 // ------------------------------------------------------------------------------
 
-var ruleTester = new RuleTester({parserOptions});
+const ruleTester = new RuleTester({parserOptions});
 ruleTester.run('boolean-prop-naming', rule, {
 
   valid: [{