Merge branch 'master' of github.com:Oshlack/splatter

* 'master' of github.com:Oshlack/splatter:
  add back libgsl-dev, if zinbwave is to be installed
  also install suggested packages on travis in order to be able to run all tests and examples
  moving zinbwave to suggests and removing  apt installation of gsl
  add back all checks
  remove comma
  temporarily reduce build time
  added apt-get dependency for zinbwave
  Add zimbwave to imports