travis: correct libdrm required regex to also track libdrm itself
travis: correct libdrm required regex to also track libdrm itself

The current regex was tracking only the libdrm_foo packages, while with
recent changed we bumped only (and rightfully so) libdrm.

Fix the regex to track any libdrm package.

Signed-off-by: Emil Velikov <f20878473f414da183da19ee25c8722cc1d711e4@collabora.com>
Reviewed-by: Andres Gomez <1948e91ee7852f22bc880d172a32ffca98fb60fa@igalia.com>
Reviewed-by: Rhys Kidd <0b3b315d08353e2046d43a86d41e3fd1dff3d6ad@gmail.com>
Reviewed-by: Eric Anholt <96f164ad4d9b2b0dacf8ebee2bb1eeb3aa69adf1@anholt.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler