Merge branch 'gitlab-ci' into 'master'

Added gitlab-ci.yml for automated testing & fixed environment-cpu.yml

See merge request !11

.gitlab-ci.yml

+stages:
+  - test
+
+test:
+  stage: test
+  image: continuumio/miniconda
+  script:
+    - conda init bash
+    - source ~/.bashrc
+    - conda env create -f environment-cpu.yml
+    - conda activate flatland-env
+    - bash test.sh

environment-cpu.yml

 name: flatland-baseline-cpu-env
 dependencies:
+    - conda-build
     - python=3.7
-    - pip=20.0
+    - libgcc
+    - pip
+    - cairo
     - pip:
         - flatland-rl==2.2.1
         - CairoSVG==2.4.2
@@ -10,4 +13,4 @@ dependencies:
         - pyhumps==1.3.1
         - wandb==0.9.2
         - ray[rllib]==0.8.5
-        - tensorflow==2.1.0
\ No newline at end of file
+        - tensorflow==2.1.0