change install method for Poetry

Author: dgarros

.travis.yml

@@ -22,7 +22,10 @@ services:
 # --------------------------------------------------------------------------
 before_script:
 - pip install invoke docker-compose
-- curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | python
+- curl -fsS -o get-poetry.py https://raw.githubusercontent.com/sdispater/poetry/master/get-poetry.py
+- python get-poetry.py --preview -y
+- source $HOME/.poetry/env
+
 script:
 - invoke build --python-ver $TRAVIS_PYTHON_VERSION
 - invoke tests --python-ver $TRAVIS_PYTHON_VERSION