Change path for bash-completion file

[havardAasen]

The current path is deprecated, and is only available for compatibility reasons. If you have pkg-configinstalled you can get the old path with pkg-config --variable=compatdir bash-completion and the new path pkg-config --variable=completionsdir bash-completion

This information can also be found in the 'bash-completion' repo https://github.com/scop/bash-completion/blob/master/README.md#faq