Relax version bounds

[dagit]

Hello and thanks for writing the glium-sdl2.

I tried to build it but I had an issue where the version bounds were too strict. I changed them to "" and now everything is working. I've been using for a while now without any issues. I'll let you decide if you want to use "" or something stricter, but either way the version bounds need a bump. This PR is for bounds of "*".

[cristicbz]

This won't work sadly, since * deps are cannot be published to crates.io . Glium and SDL2 should see v1 at some point, after which hopefully most updates will be minor and this won't break all the time. My PR #27 updates to newest versions of the libraries.