Make clang-format more aggressive

clang-format always manages to mix spaces into tab-based indentation.
Since we already require an exact tab-width of 8 it makes more sense to
use spaces.

data/solid.frag

@@ -7,5 +7,5 @@ uniform vec4 color;
 void
 main()
 {
-	gl_FragColor = color;
+        gl_FragColor = color;
 }