mesalib: Update version from 17.1.7 to 17.1.8

Release notes [1]:

> Mesa 17.1.8 Release Notes / August 28, 2017
>
> […]
>
> ### Bug fixes ###
>
> *   Bug 101910 - [BYT] ES31-CTS.functional.copy_image.non_compressed.viewclass_96_bits.rgb32f_rgb32f
> *   Bug 102308 - segfault in glCompressedTextureSubImage3D
>
> […]

[1] https://www.mesa3d.org/relnotes/17.1.8.html

mesalib.be0

@@ -1,6 +1,6 @@
 #!/usr/bin/env beesh
 
-# BEE_VERSION mesalib-17.1.7-0
+# BEE_VERSION mesalib-17.1.8-0
 
 ## this file was created by bee init and should be executed to build a
 ## bee-package. (Additional hints are located at the end of this file.)