Remove the exclusions from the pep8 CI invocation

With the codebase adhering to PEP 8, there's no longer any need to omit
certain rules when validating the pep8 convention.

Author: diogoosorio

.travis.yml

@@ -5,9 +5,9 @@ python:
   - 3.6
 install:
   - pip --version
-  - pip install -r requirements.txt
+  - pip install -r test-requirements.txt
   - pip install pep8 
 before_script:
-  - pep8 --ignore=E501,W293,E202,E241,W291   *.py 
+  - pep8 -v *.py lib/
 script:
   - pytest