Temoprarily Pin Tox Until Bug Is Fixed

https://bitbucket.org/hpk42/tox/issues/285/tox-220-breaks-some-toxini-config-files

Author: Bill Prin

.travis.yml

@@ -22,7 +22,9 @@ before_install:
 - tests/scripts/travis-before-install.sh
 
 install:
-- pip install tox coveralls
+# TODO: unpin tox when the following issue is fixed
+# https://bitbucket.org/hpk42/tox/issues/285/tox-220-breaks-some-toxini-config-files
+- pip install tox==2.0.1 coveralls
 
 script:
 - tox