Merging upstream version 2.2.0.

Signed-off-by: Daniel Baumann <daniel@debian.org>

.travis/install.sh

@@ -8,7 +8,7 @@ if [[ "$(uname -s)" == 'Darwin' ]]; then
     git clone --depth 1 https://github.com/pyenv/pyenv ~/.pyenv
     export PYENV_ROOT="$HOME/.pyenv"
     export PATH="$PYENV_ROOT/bin:$PATH"
-    eval "$(pyenv init -)"
+    eval "$(pyenv init --path)"
 
     case "${TOXENV}" in
         py36)
@@ -22,4 +22,4 @@ fi
 pip install virtualenv
 python -m virtualenv ~/.venv
 source ~/.venv/bin/activate
-pip install tox
+pip install -r requirements-dev.txt -U --upgrade-strategy only-if-needed