revert back to ruby 2.1

Originally opened at !2895 (closed) by @jameslopez.

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Revert Ruby 2.2 changes - until we solve https://gitlab.com/gitlab-org/gitlab-ce/issues/13514

This also updates Ruby 2.1.7 to 2.1.8

Restored source branch gitlab-ce-fix/revert-ruby-2.2

mentioned in merge request !2895 (closed)

/cc @jacobvosmaer

Reassigned to @rspeicher

mentioned in commit 94915f97

Status changed to merged

mentioned in commit cc314eec

Picked into 8-5-stable.

Removed ~149423 label

Mentioned in commit maxraab/gitlab-ce@cc314eec