Do not precise python version

.travis.yml

-os:
- - osx
-language: python
-python:
-  # We don't actually use the Travis Python, but this keeps it organized.
-  - "3.4"
+os: osx
 before_install:
   # Install and configure pyenv
   - ci/travis/before_install.sh

ci/travis/before_install.sh

+
+brew update
 brew install wget
 brew install libsodium
 ## Ensure your brew QT version is up to date. (brew install qt -> qt 4.8)
 brew install qt5
 brew link --force qt5
 
-
 env PYTHON_CONFIGURE_OPTS="--enable-framework" pyenv install $TRAVIS_PYTHON_VERSION
 
 pyenv shell 3.5.0