[travis] Per the Travis docs, caching the Arduino IDE may actually _hurt_ perf.

http://docs.travis-ci.com/user/caching/#How-does-the-caching-work%3F

.travis.yml

@@ -18,6 +18,4 @@ notifications:
     on_success: change
     on_failure: change
 cache:
-  ccache: true
-  directories:
-    - ../arduino-1.6.7
+  ccache: true