Fix no-GLES-on-NSGL error type and description
diff --git a/src/nsgl_context.m b/src/nsgl_context.m
index 15af835..c5539e3 100644
--- a/src/nsgl_context.m
+++ b/src/nsgl_context.m
@@ -67,8 +67,8 @@
 
     if (ctxconfig->api == GLFW_OPENGL_ES_API)
     {
-        _glfwInputError(GLFW_VERSION_UNAVAILABLE,
-                        "NSGL: This API does not support OpenGL ES");
+        _glfwInputError(GLFW_API_UNAVAILABLE,
+                        "NSGL: OpenGL ES is not available on OS X");
         return GL_FALSE;
     }