Update .travis.yml
Update .travis.yml

GLFW shouldn't need to be built as a shared library any more. Test this in the Travis build.

Also, to speed things up slightly, we don't build GLFW's libraries, examples, and docs.

nstoddard/glfw-rs,bvssvni/glfw-rs,PistonDevelopers/glfw-rs,derekdreery/glfw-rs,tomaka/glfw-rs,servo/glfw-rs,bjz/glfw-rs,mneumann/glfw-rs,derekdreery/glfw-rs