chore(release): calculate the cdnVersion on every build

The CDN version of angular is now calculated on every build,
by looking at the tags in angular/angular.js, sorting them
by semver and checking against ajax.googleapis.com which
one is available.

lib/versions/version-info.js

@@ -4,7 +4,7 @@ var shell = require('shelljs');
 var semver = require('semver');
 var _ = require('lodash');
 
-var currentPackage, previousVersions;
+var currentPackage, previousVersions, cdnVersion;
 
 
 /**
@@ -131,6 +131,29 @@ var getPreviousVersions =  function() {
   }
 };
 
+var getCdnVersion = function() {
+  return _(previousVersions)
+    .filter(function(tag) {
+      return semver.satisfies(tag, currentPackage.branchVersion);
+    })
+    .reverse()
+    .reduce(function(cdnVersion, version) {
+      if (!cdnVersion) {
+        // Note: need to use shell.exec and curl here
+        // as version-infos returns its result synchronously...
+        var cdnResult = shell.exec('curl http://ajax.googleapis.com/ajax/libs/angularjs/'+version+'/angular.min.js '+
+                  '--head --write-out "%{http_code}" -o /dev/null -silent',
+                                    {silent: true});
+        if ( cdnResult.code === 0 ) {
+          var statusCode = cdnResult.output.trim();
+          if (statusCode === '200') {
+            cdnVersion = version;
+          }
+        }
+      }
+      return cdnVersion;
+    }, null);
+}
 
 /**
  * Get the unstable snapshot version
@@ -179,4 +202,5 @@ var getSnapshotVersion = function() {
 exports.currentPackage = currentPackage = getPackage();
 exports.gitRepoInfo = gitRepoInfo = getGitRepoInfo();
 exports.previousVersions = previousVersions = getPreviousVersions();
+exports.cdnVersion = cdnVersion = getCdnVersion();
 exports.currentVersion = getTaggedVersion() || getSnapshotVersion();