Update mocha dependency

Update mocha from `^2.3.3` (currently `v2.5.3`) to `v3.2.0`.
No relevant package changes. Essentially bug fixes.

See:
- mochajs/mocha#2350 (`v3.0.0-0` release)
- https://github.com/mochajs/mocha/releases/tag/v3.2.0 (latest release)

package.json

@@ -68,7 +68,7 @@
     "inquirer": "^1.2.3",
     "is-empty-object": "^1.1.1",
     "js-yaml": "^3.5.4",
-    "mocha": "^2.3.3",
+    "mocha": "^3.2.0",
     "mocha-phantomjs": "^4.0.2",
     "motion-ui": "^1.1.0",
     "multiline": "^1.0.2",