remove __pycache__ to prevent unnecessary cache change detection.

Author: steenzout

.travis.yml

@@ -30,5 +30,5 @@ install:
 
 script:
   - tox
-  - "find ${TRAVIS_BUILD_DIR}/.tox -name log -type d | xargs -I {} rm -rf {}"
+  - "find ${TRAVIS_BUILD_DIR}/.tox -name log -o -name __pycache__ -type d | xargs -I {} rm -rf {}"