Bug 1258676 - Update to pip 8.1.1

https://pip.pypa.io/en/stable/news/
https://github.com/pypa/pip/compare/8.1.0...8.1.1

.travis.yml

@@ -21,7 +21,7 @@ matrix:
         # to work around: https://github.com/travis-ci/travis-ci/issues/4873
         - if [[ ! -f ~/venv/bin/activate ]]; then virtualenv ~/venv; fi
         - source ~/venv/bin/activate
-        - pip install -U pip==8.1.0
+        - pip install -U pip==8.1.1
       install:
         - npm install
         - pip install --disable-pip-version-check --require-hashes -r requirements/common.txt -r requirements/dev.txt
@@ -64,7 +64,7 @@ matrix:
         # Manually install mysql 5.6 since the default is v5.5.
         - sudo apt-get -qq update
         - sudo apt-get -qq install mysql-server-5.6 mysql-client-5.6 mysql-client-core-5.6
-        - pip install -U pip==8.1.0
+        - pip install -U pip==8.1.1
       install:
         - pip install --disable-pip-version-check --require-hashes -r requirements/common.txt -r requirements/dev.txt
       script:
@@ -84,7 +84,7 @@ matrix:
         # Manually install mysql 5.6 since the default is v5.5.
         - sudo apt-get -qq update
         - sudo apt-get -qq install mysql-server-5.6 mysql-client-5.6 mysql-client-core-5.6
-        - pip install -U pip==8.1.0
+        - pip install -U pip==8.1.1
       install:
         - pip install --disable-pip-version-check --require-hashes -r requirements/common.txt -r requirements/dev.txt
       script: