Changing to use shim based approach per feedback.

Per much welcomed feedback from @guybedford on #709, I have changed from using `format: global` to instead using 'shim' on the browser specific files of the bluebird repo. This is so that it does not mess with the server side implementation which _is_ CommonJS format for Node.

package-overrides/npm/bluebird@3.1.1.json

@@ -1,3 +1,7 @@
 {
-  "format": "global"
+  "shim": 
+  { 
+      "js/browser/bluebird": true,
+      "js/browser/bluebird.min": true 
+  }
 }