Fix compilation of MeshGLTest shader.
Fix compilation of MeshGLTest shader.

Precision qualifiers are not available in GLSL 1.20 and non-NVidia cards
are complaining.

MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum,MiUishadow/magnum