Remove deprecated --use-mirrors from travis.yml

The pip option `--use-mirrors` options is removed from pip since version
7.0.0 (2015-05-21), this results in a build failure on Travis. Because
PyPI is using a CDN now, an alternative to the `--use-mirrors` is not
needed so the option can be removed.

Author: ErwinJanssen

.travis.yml

@@ -20,11 +20,11 @@ before_install:
   - "sudo apt-get update -qq"
   - "sudo apt-get install nmap -qq"
 install:
-  - "pip install pep8 --use-mirrors"
-  - "pip install pyflakes --use-mirrors"
-#  - "pip install boto --use-mirrors" # disabled: since boto not supporting py3
-#  - "pip install pymongo sqlalchemy MySQL-python --use-mirrors" # disabled MySQL-python (not py3 compatible)
-  - "pip install pymongo sqlalchemy pymysql --use-mirrors"
+  - "pip install pep8"
+  - "pip install pyflakes"
+#  - "pip install boto" # disabled: since boto not supporting py3
+#  - "pip install pymongo sqlalchemy MySQL-python" # disabled MySQL-python (not py3 compatible)
+  - "pip install pymongo sqlalchemy pymysql"
   - "pip install coveralls"
   - "python setup.py install"
 before_script: