Switch to uber/npm-shrinkwrap for npm-shrinkwrap.json generation

Instead of our homegrown grunt/shrinkwrap.js
Fixes #13483.
New npm-shrinkwrap.json is human-readable but still in a consistent/stable format.
Should aid debugging, produce better diffs, and be less prone to merge conflicts

package.json

@@ -31,7 +31,6 @@
   },
   "devDependencies": {
     "btoa": "~1.1.2",
-    "canonical-json": "~0.0.4",
     "glob": "~4.0.2",
     "grunt": "~0.4.5",
     "grunt-autoprefixer": "~0.7.5",
@@ -57,6 +56,7 @@
     "grunt-sed": "~0.1.1",
     "load-grunt-tasks": "~0.5.0",
     "markdown": "~0.5.0",
+    "npm-shrinkwrap": "~3.1.3",
     "time-grunt": "~0.3.2"
   },
   "engines": {