Remove Ruby 2.1/2.2/2.3 descriptions
As Ruby 2.7 is just released, it is time to remove Ruby 2.1/2.2/2.3 (EOL-ed). Might not be bad to remove Ruby 2.4, planned to EOL in 2020-03-31.
Per code, it is the best that replacement is 2.6, which is the most stable at the beginning of 2020 unless required. Per document and non-running code, it is the best that replacement is 2.7 as it will reduce times to maintain the documents.
TODO
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Update docs !22570 (merged) -
Update more docs !27268 (merged) -
Update .gitlab-ci.ymltemplate files maintained in GitLab (/lib/gitlab/ci/templates): !23585 (merged) -
Update non-doc code !27269 (merged)
Edited by Takuya Noguchi