Update swift Docker tag to v5.8.0 (#51)

* Update swift Docker tag to v5.8.0

* Delete .gitlab-ci.yml

---------

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Christian Treffs <ctreffs@gmail.com>

.gitlab-ci.yml

@@ -1,25 +0,0 @@
-image: swift:5.1.3
-
-stages: 
-  - test
-  - build_release
-  
-build_project:
-  stage: build_release
-  script:
-    - swift package reset
-    - swift build -c release
-  tags:
-    - docker
-  only:
-    - master
-
-test_project:
-  stage: test
-  variables:
-    GIT_DEPTH: "50"
-  script:
-    - swift package reset
-    - swift test
-  tags:
-    - docker