Speed up travis execution

Author: lancergr

.travis.yml

@@ -5,12 +5,7 @@ python:
   - "3.6"
 cache: pip
 install:
-  - pip install requests
-  - pip install pycurl
-  - pip install mock
-  - pip install coveralls
-  - pip install pylint
-  - pip install pycodestyle
+  - pip install requests pycurl mock coveralls pylint pycodestyle
 script:
   - coverage run -m unittest discover -s test -p '*Test.py'
   - pycodestyle -v