pip command correction.

.travis.yml

@@ -47,7 +47,7 @@ before_install:
     -   pip install --use-mirrors matplotlib;
     - fi
 
-	- pip install --use-mirros pillow
+	- pip install --use-mirrors pillow
     - pip install --use-mirrors cython
     - pip install --use-mirrors flake8
     - pip install --use-mirrors six