update revisions.txt

Author: facchinm

build/shared/revisions.txt

@@ -29,7 +29,8 @@ ARDUINO 1.6.6
 * Bridge: YunClient.stop() now empties all buffers. Thanks @RobAtticus
 
 [core]
-AVR: fixed wrong turnOffPWM() for TIMER0B. Thanks @gonzoveliki
+* AVR: fixed wrong turnOffPWM() for TIMER0B. Thanks @gonzoveliki
+* ArduinoISP is now compatible with every architecture (not only AVR) and is much more stable. Thanks @PeterVH
 
 ARDUINO 1.6.5-r5 - 2015.08.28