Fix gitlab-ci.yml

Use python2 because scripts/gen_ir.py uses "#!/usr/bin/env python"

.gitlab-ci.yml

 image: ubuntu:16.04
 
 before_script:
-	- apt-get install build-essential python3 perl
+    - apt-get update
+    - apt-get -y install gcc make python perl git
 
-test:
-	script:
-	- make test -j
+unittests:
+    script:
+        - make test -j

README.md

@@ -20,6 +20,7 @@ Prerequisites for the build:
 * Python (2.7.x or >=3.3 are supported)
 * Perl
 * an ANSI C99 compiler (gcc, clang, icc are known to work)
+* Git
 
 ### Building with make