Merge branch 'fix-update-ruby-doc' into 'master'

Fix for update 8.10-to-8.11.md doc.

Fixed a typo in the docs to update Ruby.

See merge request !5941

doc/update/8.10-to-8.11.md

@@ -20,7 +20,31 @@ cd /home/git/gitlab
 sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
 ```
 
-### 3. Get latest code
+### 3. Update Ruby
+
+If you are you running Ruby 2.1.x, you do not _need_ to upgrade Ruby yet, but you should note that support for 2.1.x is deprecated and we will require 2.3.x in 8.13. It's strongly recommended that you upgrade as soon as possible.
+
+You can check which version you are running with `ruby -v`.
+
+Download and compile Ruby:
+
+```bash
+mkdir /tmp/ruby && cd /tmp/ruby
+curl --remote-name --progress https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.1.tar.gz
+echo 'c39b4001f7acb4e334cb60a0f4df72d434bef711  ruby-2.3.1.tar.gz' | shasum --check - && tar xzf ruby-2.3.1.tar.gz
+cd ruby-2.3.1
+./configure --disable-install-rdoc
+make
+sudo make install
+```
+
+Install Bundler:
+
+```bash
+sudo gem install bundler --no-ri --no-rdoc
+```
+
+### 4. Get latest code
 
 ```bash
 sudo -u git -H git fetch --all