add gitlab-ci yml

.gitlab-ci.yml

+image: continuumio/miniconda:latest
+
+before_script:
+  - conda install -y nose coverage
+  - conda install -y -c omnia openpathsampling
+  - conda update -y --all
+  - conda uninstall -y openpathsampling
+  - git clone https://github.com/openpathsampling/openpathsampling.git
+  - cd openpathsampling && pip install -e . && cd ..
+
+
+test:
+  script:
+          #Fix matploblib issues docker image
+          - export MPLBACKEND=PS
+          - nosetests -v --with-coverage