Update to changelog

Author: cmaglie

CHANGELOG

@@ -2,6 +2,8 @@ SAMD CORE 1.6.5
 
 * Set NVMCTRL.MANW bit to 1 (default is 0). This prevents accidental writes on program memory.
 * Bootloader: Fixed wrong UART speed (regression)
+* Fixed incorrect return value from Wire.available() when the receive buffer is not fully read.
+* Added DAC0 definition in Arduino/Genuino Zero variant file.
 
 SAMD CORE 1.6.4 2016.02.19