added multiple python version test runner

.gitlab-ci.yml

 before_script:
-  - apt-get update -qq && apt-get install -y -qq python3.6 python3-pip
-  - pip3 install -r requirements.txt
+  - apt-get update -qq
+  - apt-get install -y -qq python3.6  python3-pip
+  - git clone https://github.com/pyenv/pyenv.git ~/.pyenv
+  - export PYENV_ROOT="$HOME/.pyenv"
+  - export PATH="$PYENV_ROOT/bin:$PATH"
 
-pytestCI:
+
+test:python35:
+  script:
+    - pyenv install 3.5.9
+    - pyenv shell 3.5.9
+    - python -m pytest test
+
+
+test:python36:
+  script:
+    - pyenv install 3.6.9
+    - pyenv shell 3.6.9
+    - python -m pytest test
+
+
+test:python37:
+  script:
+    - pyenv install 3.7.5
+    - pyenv shell 3.7.5
+    - python -m pytest test
+
+
+test:python38:
   script:
-    - python3 -m pytest test
+    - pyenv install 3.8.0
+    - pyenv shell 3.8.0
+    - python -m pytest test