fix exception message

Author: MarcoCiaramella

androidgpulib/src/main/java/com/lib/androidgpulib/AndroidGPU.java

@@ -75,7 +75,7 @@ private void checkAndBuild(String glsl) throws Exception {
 
     private void checkVersion(String glsl) throws Exception {
         if (!glsl.startsWith(GLSL_VERSION)) {
-            throw new Exception("GLSL version not specified or invalid. Must be " + GLSL_VERSION);
+            throw new Exception("GLSL version not specified or invalid. First line must be " + GLSL_VERSION);
         }
     }