Fixed data_types alias description in markdown

Author: Aleksandr Kozlov

lib/puppet-strings/markdown/templates/data_type.erb

@@ -45,7 +45,11 @@
 <% end -%>
 <% end -%>
 <% if alias_of -%>
-Alias of `<%= alias_of %>`
+Alias of
+
+```puppet
+<%= alias_of %>
+```
 
 <% end -%>
 <% if params -%>