rendertests: switch gl_VertexID to gl_VertexIndex
diff --git a/tests/layer_validation_tests.cpp b/tests/layer_validation_tests.cpp
index 18c71a9..9598643 100644
--- a/tests/layer_validation_tests.cpp
+++ b/tests/layer_validation_tests.cpp
@@ -91,7 +91,7 @@
         "      vertices[0] = vec2(-1.0, -1.0);\n"
         "      vertices[1] = vec2( 1.0, -1.0);\n"
         "      vertices[2] = vec2( 0.0,  1.0);\n"
-        "   gl_Position = vec4(vertices[gl_VertexID % 3], 0.0, 1.0);\n"
+        "   gl_Position = vec4(vertices[gl_VertexIndex % 3], 0.0, 1.0);\n"
         "}\n";
 
 static const char bindStateFragShaderText[] =