Update installation and upgrade guides to use Ruby 2.3.6

Signed-off-by: Rémy Coutable <remy@rymai.me>

doc/install/installation.md

@@ -133,9 +133,9 @@ Remove the old Ruby 1.8 if present:
 Download Ruby and compile it:
 
     mkdir /tmp/ruby && cd /tmp/ruby
-    curl --remote-name --progress https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.5.tar.gz
-    echo '3247e217d6745c27ef23bdc77b6abdb4b57a118f  ruby-2.3.5.tar.gz' | shasum -c - && tar xzf ruby-2.3.5.tar.gz
-    cd ruby-2.3.5
+    curl --remote-name --progress https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.6.tar.gz
+    echo '4e6a0f828819e15d274ae58485585fc8b7caace0  ruby-2.3.6.tar.gz' | shasum -c - && tar xzf ruby-2.3.6.tar.gz
+    cd ruby-2.3.6
     ./configure --disable-install-rdoc
     make
     sudo make install

doc/update/10.1-to-10.2.md

@@ -339,11 +339,11 @@ sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
 
 If all items are green, then congratulations, the upgrade is complete!
 
-## Things went south? Revert to previous version (10.0)
+## Things went south? Revert to previous version (10.1)
 
 ### 1. Revert the code to the previous version
 
-Follow the [upgrade guide from 9.5 to 10.0](9.5-to-10.0.md), except for the
+Follow the [upgrade guide from 10.0 to 10.1](10.0-to-10.1.md), except for the
 database migration (the backup is already migrated to the previous version).
 
 ### 2. Restore from the backup

doc/update/10.2-to-10.3.md

@@ -339,11 +339,11 @@ sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
 
 If all items are green, then congratulations, the upgrade is complete!
 
-## Things went south? Revert to previous version (10.0)
+## Things went south? Revert to previous version (10.2)
 
 ### 1. Revert the code to the previous version
 
-Follow the [upgrade guide from 9.5 to 10.0](9.5-to-10.0.md), except for the
+Follow the [upgrade guide from 10.1 to 10.2](10.1-to-10.2.md), except for the
 database migration (the backup is already migrated to the previous version).
 
 ### 2. Restore from the backup