Ensure pyenv is available from home

ci/travis/build.sh

 #!/usr/bin/env bash
 
+export PYENV_ROOT="$HOME/.pyenv"
+export PATH="$PYENV_ROOT/bin:$PATH"
 eval "$(pyenv init -)"
 
 cd $HOME/build/duniter/sakia

ci/travis/test.sh

 #!/usr/bin/env bash
 
+export PYENV_ROOT="$HOME/.pyenv"
+export PATH="$PYENV_ROOT/bin:$PATH"
 eval "$(pyenv init -)"
 
 if [ $TRAVIS_OS_NAME == "linux" ]