start ubuntu and install clang

.gitlab-ci.yml

@@ -1,16 +1,9 @@
-# This file is a template, and might need editing before it works on your project.
+image: ubuntu:18.04
-# use the official gcc image, based on debian
-# can use verions as well, like gcc:5.2
-# see https://hub.docker.com/_/gcc/
-image: walberla/buildenv-ubuntu-clang
 
 build:
   stage: build
-  # instead of calling g++ directly you can also use some build toolkit like make
-  # install the necessary build tools when needed
-  # before_script: 
-  #   - apt update && apt -y install make autoconf 
   script:
+    - apt-get update -qq && apt-get install -y -qq git make clang
     - CC=clang CXX=clang++ make
   artifacts:
     paths: