Bump ruby 2.3.6 cache key and source installation docs

.gitlab-ci.yml

@@ -6,7 +6,7 @@ image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.3.7-golang-1.9-git
     - gitlab-org
 
 .default-cache: &default-cache
-  key: "ruby-2.3.6-with-yarn"
+  key: "ruby-2.3.7-with-yarn"
   paths:
     - vendor/ruby
     - .yarn-cache/
@@ -571,7 +571,7 @@ static-analysis:
   script:
     - scripts/static-analysis
   cache:
-    key: "ruby-2.3.6-with-yarn-and-rubocop"
+    key: "ruby-2.3.7-with-yarn-and-rubocop"
     paths:
       - vendor/ruby
       - .yarn-cache/

doc/install/installation.md

@@ -133,9 +133,10 @@ 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-2.3.6.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
+    curl --remote-name --progress https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.7.tar.gz
+    echo '540996fec64984ab6099e34d2f5820b14904f15a  ruby-2.3.7.tar.gz' | shasum -c - && tar xzf ruby-2.3.7.tar.gz
+    cd ruby-2.3.7
+
     ./configure --disable-install-rdoc
     make
     sudo make install