Default to in-memory storage for the proxy (#475)

* Default to in-memory storage for the proxy

This makes it easier for someone to try out or just run the proxy by
executing the binary without further environment setup.

* Remove obsolete comment

cmd/proxy/.env

@@ -1,3 +1,4 @@
 ATHENS_MONGO_STORAGE_URL=mongodb://127.0.0.1:27017
+ATHENS_STORAGE_TYPE=mongo
 GO_ENV=test_postgres
 POP_PATH=$PWD/cmd/proxy

cmd/proxy/actions/storage.go

@@ -18,8 +18,7 @@ import (
 
 // GetStorage returns storage backend based on env configuration
 func GetStorage() (storage.BackendConnector, error) {
-	// changing to mongo storage, memory seems buggy
-	storageType := env.StorageTypeWithDefault("mongo")
+	storageType := env.StorageTypeWithDefault("memory")
 	var storageRoot string
 	var err error