Update changelog

CHANGELOG.md

+# v0.2.0 (2018-08-10)
+
+* Corrected 'on' value for lights
+* Output for 'version' command goes to stdout
+* Add metrics for failures
+* Added HTTP timeouts
+* Added 'device_id' field to sensors
+* Add ability to map motion sensor name to temperature and light sensors in the same device
+
 # v0.1.0 (2018-08-04)
 
 Initial release