travis: Use requirement files for pip

This way we can pin tox/pip versions (which are used in the native
Travis environment) *and* get notified about updates by requires.io.

scripts/dev/ci/requirements-travis.txt

@@ -0,0 +1,3 @@
+pip==8.1.1  # rq.filter: != 8.1.2
+codecov==2.0.3
+tox==2.3.1

scripts/dev/ci/travis_install.sh

@@ -52,9 +52,7 @@ brew_install() {
 }
 
 pip_install() {
-    # Make sure pip is up-to-date first
-    travis_retry sudo -H python3 -m pip install -U pip
-    travis_retry sudo -H python3 -m pip install -U "$@"
+    travis_retry sudo -H python3 -m pip install -r scripts/dev/ci/requirements-travis.txt
 }
 
 npm_install() {
@@ -84,7 +82,7 @@ elif [[ $TRAVIS_OS_NAME == osx ]]; then
     # Disable App Nap
     defaults write NSGlobalDomain NSAppSleepDisabled -bool YES
     brew_install python3 pyqt5
-    pip_install tox
+    pip_install
     check_pyqt
     exit 0
 fi
@@ -94,31 +92,25 @@ pyqt_pkgs="python3-pyqt5 python3-pyqt5.qtwebkit"
 case $TESTENV in
     py34-cov)
         apt_install python3-pip xvfb $pyqt_pkgs
-        pip_install tox codecov
         check_pyqt
         ;;
     pylint|vulture)
         apt_install python3-pip $pyqt_pkgs
-        pip_install tox
         check_pyqt
         ;;
     flake8)
         # We need an up-to-date Python because of:
         # https://github.com/google/yapf/issues/46
         apt_install -t trusty-updates python3.4 python3-pip
-        pip_install tox
         ;;
     docs)
         apt_install python3-pip $pyqt_pkgs asciidoc
-        pip_install tox
         check_pyqt
         ;;
     misc|pyroma|check-manifest)
-        pip_install tox
         ;;
     eslint)
         apt_install python3-pip npm nodejs nodejs-legacy
-        pip_install tox
         npm_install eslint
         ;;
     *)
@@ -126,3 +118,5 @@ case $TESTENV in
         exit 1
         ;;
 esac
+
+pip_install