Throws error after building the functions

As you said in readme "For most use cases you should NOT need to do any configuration." I didn't change any configuration. Should I?
It builds each function that I have specified in serverless.yml but in the end, it throws the following error: 

```EEXIST: file already exists, symlink '../JSONStream/bin.js' -> '/tmp/warnings/node_modules/.bin/JSONStream'```