Remove duplicate "pip install -r requirements.txt"

Author: jpvanhal

.travis.yml

@@ -5,8 +5,6 @@ python:
   - pypy
   - 3.3
   - 3.4
-before_script:
-  - pip install -r requirements.txt
 script:
   - flake8 .
   - isort --recursive --diff . && isort --recursive --check-only .