changed mercury extension to .mercury, to avoid conflict with Obj-C

lib/linguist/languages.yml

@@ -1096,17 +1096,12 @@ Mercury:
   type: programming
   # This is the background colour on the web page.
   color: "#abcdef"
-  primary_extension: .m
+  # The primary extension is .m, but lingist won't accept duplicates
-  # Mercury's syntax is not prolog syntax, but they do share the lexer
+  primary_extension: .mercury
-  lexer: Prolog
-
-Mercury:
-  type: programming
-  # This is the background colour on the web page.
-  color: "#abcdef"
-  primary_extension: .m
   # Mercury's syntax is not prolog syntax, but they do share the lexer
   lexer: Prolog
+  extensions:
+  - .m
 
 MiniD: # Legacy
   searchable: false

lib/linguist/vendor.yml

@@ -41,6 +41,7 @@
 - foundation.css
 
 # Vendored dependencies
+- thirdparty/
 - vendors?/
 
 # Debian packaging