Use gitlab to trigger releases in pipeline

[wren]

Neither Travis Github Actions support manually triggering a pipeline step, so
this PR adds that step to Gitlab. It just increments the version, commits and
tags the release. Our regular Travis release process will take over after the
tag is pushed.

Checklist

• The code change is tested and works locally.
• Tests pass. Your PR cannot be merged unless tests pass. --
  poetry run behave
• The code passes linting via
  black (consistent code styling). --
  poetry run black --check . --verbose --diff
• The code passes linting via pyflakes
  (logically errors and unused imports). -- poetry run pyflakes jrnl features
• There is no commented out code in this PR.
• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open
  Pull Requests for the same update/change?
• Have you added an explanation of what your changes do and why you'd like
  us to include them?
• Have you written new tests for your core changes, as applicable?