message: fix test get_transform_feedback_varyings
  Test failed to create program with "OpenGL does not allow varying of
  type int" caused by "varying int color;". Changed to float.
  Test also specified the wrong id for the attribute.
diff: @@ -370,11 +370,11 @@ fn get_transform_feedback_varyings() {
  #version 110
  varying vec2 normal;
  - varying int color;
  + varying float color;
  void main() {
  normal = vec2(0.0, 0.0);
  - color = 5;
  + color = 5.0;
  gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
  }
  @@ -415,13 +415,13 @@ fn get_transform_feedback_varyings() {
  assert_eq!(program.get_transform_feedback_buffers()[1],
  glium::program::TransformFeedbackBuffer {
  - id: 0,
  + id: 1,
  stride: 4,
  elements: vec![glium::program::TransformFeedbackVarying {
  name: "color".to_string(),
  offset: 0,
  size: 4,
  - ty: glium::vertex::AttributeType::U32,
  + ty: glium::vertex::AttributeType::F32,
  }]
  });
  