Add colon to example descriptions

pages/common/ruby.md

@@ -10,14 +10,14 @@
 
 `ruby {{script.rb}}`
 
-- Execute a single command in the command line
+- Execute a single command in the command line:
 
 `ruby -e {{command}}`
 
-- Check if the given Ruby script is written correctly (Syntax check)
+- Check if the given Ruby script is written correctly (Syntax check):
 
 `ruby -c {{script.rb}}`
 
-- Show the version of Ruby you are using
+- Show the version of Ruby you are using:
 
 `ruby -v`