Remove --upgrade option

Author: style95

.travis.yml

@@ -57,7 +57,7 @@ before_install:
   - ./tools/travis/docker.sh
   - sudo apt-get install -y python3-pip
   - pip install --user --upgrade pip setuptools six
-  - pip3 install --user --upgrade pip setuptools six
+  - pip3 install --user setuptools six
 
 install:
   - ./tools/travis/setup.sh