More Travis fixing...

include/global.h

@@ -74,7 +74,8 @@ typedef enum {
 #ifdef _WIN32
 #include <windows.h>
 #endif
-#include <GL/gl3.h>
+#include <GL/gl.h>
+#include <GL/glext.h>
 #endif
 
 // If available, use our own assert that prints the call stack