change dir for build output or cleanup dir before new builds

[kevinm6]

When a new update (commit) is available, and Lazy updates the plugin it brings it in a detached HEAD because of course with :build command that follow the installation it creates new files in the directory of the plugin.

I think that is possible to manage this in some ways:

• add a .gitignore file to ignore generated file from the build (.rocks/)
• change directory for the build output (this leads to update the rtp path)