Update pyenv to 2.6.9

Brings support for newer Python versions

Author: jb3

Dockerfile

@@ -29,7 +29,7 @@ RUN apt-get -y update \
         tk-dev \
     && rm -rf /var/lib/apt/lists/*
 
-RUN git clone -b v2.6.5 --depth 1 https://github.com/pyenv/pyenv.git $PYENV_ROOT
+RUN git clone -b v2.6.9 --depth 1 https://github.com/pyenv/pyenv.git $PYENV_ROOT
 
 COPY --link scripts/build_python.sh /