Add jsonc alias to JSONDOC lexer (#1440)

GitHub supports the use of the `jsonc` info string to permit comments
in JSON. The Rouge JSONDOC lexer provides a lexer that would lex this
correctly but which does not support the use of `jsonc` as an alias.
This commit adds that alias.

lib/rouge/lexers/json_doc.rb

@@ -8,6 +8,7 @@ module Lexers
     class JSONDOC < JSON
       desc "JavaScript Object Notation with extensions for documentation"
       tag 'json-doc'
+      aliases 'jsonc'
 
       prepend :name do
         rule %r/([$\w]+)(\s*)(:)/ do