Update revision log

Author: cmaglie

build/shared/revisions.txt

@@ -2,6 +2,8 @@ ARDUINO 1.6.11
 
 [ide]
 * Fixed a serious bug that prevented some 3rd party boards, installed through external index.json URL, to work correctly.
+* Fixed a bug in boards manager that, in some rare circumstances, could lead to remove bundled
+  tools when uninstalling a previously installed AVR core.
 * builder: fixed regression about inclusion of files in subfolders of the sketch
   (see https://github.com/arduino/Arduino/issues/5186 for details)
 * avrdude: reverted to version 6.0.1, until all discovered regressions are solved