fix(README): remove commons-ui from auto-build enabled

The camunda-commons-ui repository is only aimed
to provide libraries or utilities for the other UI aspects
of the webapps, it does not have to be build.

Related to: 
https://groups.google.com/d/msg/camunda-bpm-dev/Ctmc3sQSfxc/xkTrM1tWQ4EJ