PyPI now has CDN; Travis shouldn't use mirrors

Now that PyPI utilizes a CDN, the "--use-mirrors" setting slows down the
install process and has essentially been deprecated.

.travis.yml

@@ -8,7 +8,7 @@ before_install:
  - sudo locale-gen fr_FR.UTF-8 tr_TR.UTF-8
 install:
     - if [[ $TRAVIS_PYTHON_VERSION == '2.7' ]]; then ln -s /usr/share/asciidoc/asciidocapi.py ~/virtualenv/python2.7/lib/python2.7/site-packages/; fi
-    - pip install mock --use-mirrors
-    - pip install . --use-mirrors
-    - pip install --use-mirrors Markdown
+    - pip install mock
+    - pip install .
+    - pip install Markdown
 script: python -m unittest discover