fix doctest

Author: Manishearth

src/doc/trpl/documentation.md

@@ -15,7 +15,7 @@ comments":
 // the "link" crate attribute is currently required for rustdoc, but normally
 // isn't needed.
 #![crate_id = "universe"]
-#![crate_type= lib"]
+#![crate_type= "lib"]
 
 //! Tools for dealing with universes (this is a doc comment, and is shown on
 //! the crate index page. The ! makes it apply to the parent of the comment,