Update ruby version to 2.1.2, fixes #362 related to #360

doc/install/installation.md

@@ -95,8 +95,8 @@ Remove the old Ruby 1.8 if present
 Download Ruby and compile it:
 
     mkdir /tmp/ruby && cd /tmp/ruby
-    curl --progress ftp://ftp.ruby-lang.org/pub/ruby/2.0/ruby-2.0.0-p481.tar.gz | tar xz
-    cd ruby-2.0.0-p481
+    curl --progress ftp://ftp.ruby-lang.org/pub/ruby/2.1/ruby-2.1.2.tar.gz | tar xz
+    cd ruby-2.1.2
     ./configure --disable-install-rdoc
     make
     sudo make install