chore(docs-gen): create plnkr examples with the correct version

- docs for the snapshot will include the snapshot files from code.angularjs.org
- docs for tagged versions will include the files from the (Google) CDN
- docs for local / untagged versions will try to include the files from the (Google) CDN, which will fail. This gives immediate feedback that something is broken.

Closes #15267
Closes #15358

docs/config/services/deployments/production.js

@@ -1,16 +1,30 @@
 'use strict';
 
 var versionInfo = require('../../../../lib/versions/version-info');
-var cdnUrl = '//ajax.googleapis.com/ajax/libs/angularjs/' + versionInfo.cdnVersion;
+
+var googleCdnUrl = '//ajax.googleapis.com/ajax/libs/angularjs/';
+var angularCodeUrl = '//code.angularjs.org/';
+
+var cdnUrl = googleCdnUrl + versionInfo.cdnVersion;
+
+// The plnkr examples must use the code.angularjs.org repo for the snapshot,
+// and the cdn for the tagged version and, if the build is not tagged, the currentVersion.
+//
+// The currentVersion may not be available on the cdn (e.g. if built locally, or hasn't been pushed
+// yet). This will lead to a 404, but this is preferable to loading a version with which the example
+// might not work (possibly in subtle ways).
+var examplesCdnUrl = versionInfo.isSnapshot ?
+  (angularCodeUrl + 'snapshot') :
+  (googleCdnUrl + (versionInfo.version || versionInfo.currentVersion));
 
 module.exports = function productionDeployment(getVersion) {
   return {
     name: 'production',
     examples: {
       commonFiles: {
-        scripts: [cdnUrl + '/angular.min.js']
+        scripts: [examplesCdnUrl + '/angular.min.js']
       },
-      dependencyPath: cdnUrl + '/'
+      dependencyPath: examplesCdnUrl + '/'
     },
     scripts: [
       cdnUrl + '/angular.min.js',