message: Remove redundant mut
  Appeases the clippy::unnecessary_mut_passed lint.
diff: @@ -55,13 +55,13 @@ pub fn build_shader<F: ?Sized>(facade: &F, shader_type: gl::types::GLenum, sourc
  -> Result<Shader, ProgramCreationError> where F: Facade
  {
  unsafe {
  - let mut ctxt = facade.get_context().make_current();
  + let ctxt = facade.get_context().make_current();
  if ctxt.capabilities.supported_glsl_versions.is_empty() {
  return Err(ProgramCreationError::CompilationNotSupported);
  }
  - if !check_shader_type_compatibility(&mut ctxt, shader_type) {
  + if !check_shader_type_compatibility(&ctxt, shader_type) {
  return Err(ProgramCreationError::ShaderTypeNotSupported);
  }
  @@ -187,13 +187,13 @@ pub fn build_spirv_shader<F: ?Sized>(facade: &F, shader_type: gl::types::GLenum,
  -> Result<Shader, ProgramCreationError> where F: Facade
  {
  unsafe {
  - let mut ctxt = facade.get_context().make_current();
  + let ctxt = facade.get_context().make_current();
  if ctxt.capabilities.supported_glsl_versions.is_empty() {
  return Err(ProgramCreationError::CompilationNotSupported);
  }
  - if !check_shader_type_compatibility(&mut ctxt, shader_type) {
  + if !check_shader_type_compatibility(&ctxt, shader_type) {
  return Err(ProgramCreationError::ShaderTypeNotSupported);
  }
  