Syntax highlighting for spawn_ functions

* `spawn_link`
* `spawn_monitor`

syntax/elixir.vim

@@ -15,9 +15,9 @@ syn cluster elixirNotTop contains=@elixirRegexSpecial,@elixirStringContained,@el
 syn match elixirComment '#.*' contains=elixirTodo
 syn keyword elixirTodo FIXME NOTE TODO OPTIMIZE XXX HACK contained
 
-syn keyword elixirKeyword case when cond for if unless try receive spawn send
+syn keyword elixirKeyword case when cond for if unless try receive send
 syn keyword elixirKeyword exit raise throw after rescue catch else do end
-syn keyword elixirKeyword quote unquote super
+syn keyword elixirKeyword quote unquote super spawn spawn_link spawn_monitor
 
 " Functions used on guards
 syn keyword elixirKeyword contained is_atom is_binary is_bitstring is_boolean