update .travis.yml to run pep8 check

.travis.yml

@@ -14,6 +14,10 @@ env:
   - GEVENT_RESOLVER=ares GEVENT_BACKEND=signalfd
   - GEVENT_RESOLVER=ares GEVENT_FILE=thread
   - NWORKERS=1 TESTS="*dns*.py" GEVENT_RESOLVER=ares GEVENTARES_SERVERS=8.8.8.8
+matrix:
+  include:
+    - python: 2.7
+      env: TESTS=xtest_pep8.py INSTALL_PEP8=1
 install:
  - deactivate
  - export VER=$TRAVIS_PYTHON_VERSION
@@ -30,6 +34,7 @@ install:
  - sudo dpkg -i python$VER-psycopg2_2.4.5_i386.deb
  - sudo dpkg -i python$VER-pysendfile_2.0.0_i386.deb
  - tar -xf web.py-0.37.tar.gz && cd web.py-0.37 && sudo $PYTHON setup.py -q install && cd -
+ - if [[ $INSTALL_PEP8 == '1' ]]; then sudo pip install --use-mirrors -q pep8; fi
  - cython --version
  - $PYTHON -c 'import greenlet; print greenlet, greenlet.__version__; import psycopg2; print psycopg2, psycopg2.__version__; import web; print web, web.__version__'
  - "echo `date`: Started installing gevent"