Stub out logger in tests

services/docstore/test/unit/coffee/MongoManagerTests.coffee

@@ -12,6 +12,7 @@ describe "MongoManager", ->
 				db: @db = { docs: {}, docOps: {} }
 				ObjectId: ObjectId
 			'metrics-sharelatex': {timeAsyncMethod: sinon.stub()}
+			'logger-sharelatex': {log: ()->}
 		@project_id = ObjectId().toString()
 		@doc_id = ObjectId().toString()
 		@callback = sinon.stub()