message: update changelog for fw release
diff: # Unreleased Features
  Please add a note of your changes below this heading if you make a Pull Request.
  -## UNRELEASED
  +# Releases
  +## [0.4.2] - 2018-07-04
  ### Added
  * Hall sensor feedback
  * Configurable RC PWM input
  @@ -11,7 +12,6 @@ Please add a note of your changes below this heading if you make a Pull Request.
  * `motor.config.current_control_bandwidth` and `motor.set_current_control_bandwidth`. Latter required to invoke gain recalculation.
  * `encoder.config.bandwidth`
  -# Releases
  ## [0.4.1] - 2018-07-01
  ### Fixed
  * Encoder errors would show up as Axis error `ERROR_MOTOR_FAILED` instead of `ERROR_ENCODER_FAILED`.
  