Pin dependencies with npm shrinkwrap

* Use `npm run shrinkwrap` to create a shrinkwrap file with all dependencies pinned
* Update dependency `source-map` to latest (Closes #738)

package.json

@@ -30,7 +30,7 @@
   ],
   "dependencies": {
     "async": "~0.2.6",
-    "source-map": "0.1.34",
+    "source-map": "~0.5.1",
     "uglify-to-browserify": "~1.0.0",
     "yargs": "~3.5.4"
   },
@@ -46,6 +46,7 @@
     ]
   },
   "scripts": {
+    "shrinkwrap": "rm ./npm-shrinkwrap.json; rm -rf ./node_modules; npm i && npm shrinkwrap && npm outdated",
     "test": "node test/run-tests.js"
   }
 }