travisci: remove sudo command to use cache

.travis.yml

@@ -8,6 +8,12 @@ php:
   - 7.0
   - hhvm
 
+cache:
+  directories:
+    - $HOME/.composer
+    - $HOME/.cache/pip
+    - vendor
+
 env:
     global:
         - SYMFONY_DEPRECATIONS_HELPER=weak
@@ -38,7 +44,8 @@ before_script:
   - if [ "$SYMFONY_VERSION" = "2.8.*@dev" ] || [ "$SYMFONY_VERSION" = "3.0.x-dev as 2.8" ]; then SYMFONY_DEPRECATIONS_HELPER=strict; fi;
   - if [ "$SYMFONY_VERSION" != "" ]; then composer require "symfony/symfony:${SYMFONY_VERSION}" --no-update; fi;
   - travis_wait composer update --prefer-source --no-interaction $COMPOSER_FLAGS
-  - sudo pip install -r Resources/doc/requirements.txt
+  - export PATH=$HOME/.local/bin:$PATH
+  - pip install -r Resources/doc/requirements.txt --user `whoami`
 
 script: make test