Update 3.0.md

x-type for external docs

Author: amrapalijz

versions/3.0.md

@@ -1028,11 +1028,11 @@ Field Name | Type | Description
 - description: Find more info here
   url: https://example.com
   type: website
-- type: api documentation
+- x-type: api documentation
   url: http://example.org/api/docs
-- type: publication
+- x-type: publication
   url: https://doi.org/10.1093/nar/gks1114
-- type: social media
+- x-type: social media
   url: http://twitter.com/mypetstore
 ```