add grunt-cli to gitlab-ci

2 jobs for feature/produkthaftung in 53 seconds (queued for 8 seconds)
Status Job ID Name Coverage
  Build
failed #32602
build

00:00:53

 
  Publish
skipped #32603
publish
 
Name Stage Failure
failed
build Build
Loading "sass.js" tasks...ERROR
>> Error: Node Sass does not yet support your current environment: Linux 64-bit with Unsupported runtime (83)
>> For more information on which environments are supported please see:
>> https://github.com/sass/node-sass/releases/tag/v4.9.0
Warning: Task "sass" not found. Use --force to continue.

Aborted due to warnings.
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1