Revert "Add code coverage for JS"

This reverts commit e295bf1.

Istanbul doesn't support ES6-style "import" declarations, which I'm
using.

.travis.yml

@@ -1,5 +1,4 @@
 language: node_js
 node_js: node
 git:
-    submodules: false
-after_script: NODE_ENV=test istanbul cover ./node_modules/mocha/bin/_mocha --report lcovonly -- -R spec && cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js && rm -rf ./coverage
+    submodules: false

package.json

@@ -28,9 +28,7 @@
     "babel-register": "^6.3.13",
     "babelify": "^7.2.0",
     "chai": "^3.4.1",
-    "coveralls": "^2.11.6",
     "gulp-util": "^3.0.7",
-    "istanbul": "^0.4.2",
     "mocha": "^2.3.4",
     "sinon": "^1.17.2",
     "sinon-chai": "^2.8.0",