chore: Properly detect files as GLSL on GitHub

.gitattributes

@@ -4,6 +4,10 @@
 # Set *.as files as ActionScript, vs. GitHub's guess of AngelScript
 *.as   linguist-language=ActionScript
 
+# Properly detect files as GLSL on Github
+*.frag			linguist-language=GLSL
+*.vert			linguist-language=GLSL
+
 # Binary files
 *.png  binary
 *.fla  binary