Merge branch 'ruby_sha' into 'master'

Fix Ruby SHA in installation guide

The Ruby SHA that we were checking against in the
installation guide was wrong. I replaced it with
sha256sum which is also present in the Ruby downloads
page. Also added it as a note in the doc styleguide. 

See merge request !2726

doc/development/doc_styleguide.md

@@ -120,6 +120,17 @@ Inside the document:
   `http://doc.gitlab.com/ce/administration/restart_gitlab.html`.
   Replace `reconfigure` with `restart` where appropriate.
+## Installation guide
+
+- **Ruby:**
+  In [step 2 of the installation guide](../install/installation.md#2-ruby),
+  we install Ruby from source. Whenever there is a new version that needs to
+  be updated, remember to change it throughout the codeblock and also replace
+  the sha256sum (it can be found in the [downloads page][ruby-dl] of the Ruby
+  website).
+
+[ruby-dl]: https://www.ruby-lang.org/en/downloads/ "Ruby download website"
+
 ## API
 Here is a list of must-have items. Use them in the exact order that appears

doc/install/installation.md

@@ -124,7 +124,7 @@ Download Ruby and compile it:
     mkdir /tmp/ruby && cd /tmp/ruby
     curl -O --progress https://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.4.tar.gz
-    echo 'e2e195a4a58133e3ad33b955c829bb536fa3c075  ruby-2.2.4.tar.gz' | shasum -c - && tar xzf ruby-2.2.4.tar.gz
+    echo 'b6eff568b48e0fda76e5a36333175df049b204e91217aa32a65153cc0cdcb761  ruby-2.2.4.tar.gz' | sha256sum -c - && tar xzf ruby-2.2.4.tar.gz
     cd ruby-2.2.4
     ./configure --disable-install-rdoc
     make