Removes GCS Adapter from provided adapters

* 💣 removes exposed GCS files adapter

- Should fix problems with GCS
- Throws error that shows the right repo

src/deprecated.js

@@ -0,0 +1,5 @@
+export function useExternal(name, moduleName) {
+  return function() {
+    throw `${name} is not provided by parse-server anymore; please install ${moduleName}`;
+  }
+}

src/index.js

@@ -1,8 +1,8 @@
 import winston           from 'winston';
 import ParseServer       from './ParseServer';
-import GCSAdapter        from 'parse-server-gcs-adapter';
-import S3Adapter         from 'parse-server-s3-adapter';
-import FileSystemAdapter from 'parse-server-fs-adapter';
+import S3Adapter         from 'parse-server-s3-adapter'
+import FileSystemAdapter from 'parse-server-fs-adapter'
+import { useExternal }   from './deprecated'
 
 if (process.env.VERBOSE || process.env.VERBOSE_PARSE_SERVER) {
   winston.level = 'silly';
@@ -20,5 +20,7 @@ let _ParseServer = function(options) {
 // Mount the create liveQueryServer
 _ParseServer.createLiveQueryServer = ParseServer.createLiveQueryServer;
 
+let GCSAdapter = useExternal('GCSAdapter', 'parse-server-gcs-adapter');
+
 export default ParseServer;
 export { S3Adapter, GCSAdapter, FileSystemAdapter, _ParseServer as ParseServer };