travis: Don't install pep8 manually

.travis.yml

@@ -12,7 +12,7 @@ before_install:
     - sleep 3
 install:
     - pip install lupa --install-option='--no-luajit'
-    - pip install cffi flake8 pep8 pyflakes pep8-naming
+    - pip install cffi flake8 pyflakes pep8-naming
     - pip install -e ".[web,hidtrigger,autorotate,chdkcamera]"
     - pip install -r test-requirements.txt
     - pip install -e .