Remove including python 2.7 with mock package

Author: Anton Prokhorov

.travis.yml

@@ -12,9 +12,6 @@ env:
 - PACKAGES="django>=1.9,<1.10"
 - PACKAGES="django>=1.10,<1.11"
 matrix:
- include:
- - python: '2.7'
- env: PACKAGES="mock==2.0.0"
  exclude:
  - python: '3.3'
  env: PACKAGES="django>=1.9,<1.10"