Update docs for Ruby MRI 2.1 requirement

Updates `7-13-stable` with changes from !1089

Closes #2135

See merge request !1109

7-13-5-stable candidate



See merge request !1145

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This reverts commit 7bde6ae5.

This reverts commit 5a1aa49b, reversing
changes made to a675bea2.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This reverts commit 734a4ba8.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This reverts commit 27a15850.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This reverts commit 54113319.

This reverts commit 3d416f16.

This reverts commit 435f680b.

This reverts commit dfccb06d.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This reverts commit d24c40ec.

This reverts commit 459e6d34, reversing
changes made to 804168e1.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Update 7-13-stable with 7.13.4



See merge request !1113

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Update stable 7.13.3



See merge request !1088

Update stable for 7.13.2



See merge request !1056

- The "Edit" form didn't have Markdown hints.
- The "New" form had a paperclip icon for attachments, the "edit" form
  didn't.

Closes #2010

Closes internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2525

Starting with migration `20150717130904` commit count is stored in the
database. For existing projects it defaults to `0` and is updated to the
correct value when commits are pushed.

The newly introduced rake task updates the commit count for all projects
which have not been updated yet.

Refs !986, !989, #2040.

Closes #2013

Closes #2092