Updates Travis configuration to use latest pypy

Author: sdispater

.travis.yml

@@ -28,6 +28,19 @@ before_install:
   - pip install codecov
 
 install:
+  - |
+      if [ "$TRAVIS_PYTHON_VERSION" = "pypy" ]; then
+        export PYENV_ROOT="$HOME/.pyenv"
+        if [ -f "$PYENV_ROOT/bin/pyenv" ]; then
+          pushd "$PYENV_ROOT" && git pull && popd
+        else
+          rm -rf "$PYENV_ROOT" && git clone --depth 1 https://github.com/yyuu/pyenv.git "$PYENV_ROOT"
+        fi
+        export PYPY_VERSION="5.4.1"
+        "$PYENV_ROOT/bin/pyenv" install --skip-existing "pypy-$PYPY_VERSION"
+        virtualenv --python="$PYENV_ROOT/versions/pypy-$PYPY_VERSION/bin/python" "$HOME/virtualenvs/pypy-$PYPY_VERSION"
+        source "$HOME/virtualenvs/pypy-$PYPY_VERSION/bin/activate"
+      fi
   - pip install -r tests-requirements.txt
   - python setup.py develop