chore(doc-gen): improve github links to point to the correct tagged URL

Closes #1994

package.json

@@ -1,6 +1,7 @@
 {
   "name": "angular",
   "version": "2.0.0-alpha.25",
+  "branchPattern": "2.0.*",
   "description": "Angular 2 - a web framework for modern web apps",
   "homepage": "https://github.com/angular/angular",
   "bugs": "https://github.com/angular/angular/issues",
@@ -105,6 +106,7 @@
     "rewire": "^2.3.3",
     "run-sequence": "^1.1.0",
     "semver": "^4.3.4",
+    "shelljs": "^0.5.0",
     "sorted-object": "^1.0.0",
     "source-map": "^0.3.0",
     "sprintf-js": "1.0.*",