miniconda/install_miniconda.sh: Add `libXext6`, required for Qt4, to ensure it is installed.
miniconda/install_miniconda.sh: Add `libXext6`, required for Qt4, to ensure it is installed.

jakirkham/docker_ubuntu_drmaa_conda,DudLab/docker_centos_drmaa_conda,nanshe-org/docker_centos_drmaa_conda,jakirkham/docker_basic,jakirkham/docker_centos_drmaa_conda