Merge pull request #12315 from twbs/use-shrinkwrap

Do npm caching based on npm-shrinkwrap.canonical.json

package.json

@@ -27,6 +27,7 @@
   "devDependencies": {
     "browserstack-runner": "~0.0.15",
     "btoa": "~1.1.1",
+    "canonical-json": "~0.0.3",
     "grunt": "~0.4.2",
     "grunt-banner": "~0.2.0",
     "grunt-contrib-clean": "~0.5.0",
@@ -42,6 +43,7 @@
     "grunt-contrib-uglify": "~0.3.0",
     "grunt-contrib-watch": "~0.5.3",
     "grunt-csscomb": "~2.0.1",
+    "grunt-exec": "0.4.3",
     "grunt-html-validation": "~0.1.13",
     "grunt-jekyll": "~0.4.1",
     "grunt-jscs-checker": "~0.3.0",