Merge pull request #31 from xyproto/master

Removing the parenthesis made scheme work on Arch Linux again
Fix misleading arguments of Cairo::Context#set_source_rgb
Fix redirection
Hide warnings if apt-get is not installed
Merge pull request #29 from pczarn/fix

Fix arguments, redirect stderr
With these changes, the full chain works on Arch Linux
With these changes, the full chain works on Arch Linux