Merge branch 'update_ruby' into 'master'

Update ruby

The old version of ruby can be installed on the recent ubunntu releases because of incompatibility with readline.

http://stackoverflow.com/questions/23488790/compile-ruby-2-0-errors-without-rvm-or-rbenv-readline-c188626-error-func

See merge request !16

README.md

@@ -46,8 +46,8 @@ a) Linux
 ```bash
 mkdir /tmp/ruby && cd /tmp/ruby
-curl --progress ftp://ftp.ruby-lang.org/pub/ruby/2.0/ruby-2.0.0-p353.tar.gz | tar xz
-cd ruby-2.0.0-p353
+curl --progress http://cache.ruby-lang.org/pub/ruby/2.1/ruby-2.1.5.tar.gz | tar xz
+cd ruby-2.1.5
 ./configure --disable-install-rdoc
 make
 sudo make install