Fix a conflict between two Babel plugins

The transform-async-to-promises Babel plugin could end up inserting helper code
between the `@ngInject` comment and the associated function, breaking
the functionality of the angularjs-annotate Babel plugin. Work around
this by adding the `$inject` property to the function manually instead
of relying on the angularjs-annotate plugin to do it.

This issue only showed up locally when testing out a change to convert
the module's imports to ES module syntax.

src/sidebar/services/oauth-auth.js

@@ -21,7 +21,6 @@ const serviceConfig = require('../service-config');
  * Interaction with OAuth endpoints in the annotation service is delegated to
  * the `OAuthClient` class.
  */
-// @ngInject
 function auth(
   $rootScope,
   $window,
@@ -300,4 +299,17 @@ function auth(
   };
 }
 
+// `$inject` is added manually rather than using `@ngInject` to work around
+// a conflict between the transform-async-to-promises and angularjs-annotate
+// Babel plugins.
+auth.$inject = [
+  '$rootScope',
+  '$window',
+  'OAuthClient',
+  'apiRoutes',
+  'flash',
+  'localStorage',
+  'settings',
+];
+
 module.exports = auth;