Exclude indoc invocations in test code from rustfmt

Author: dtolnay

tests/tests/run-pass.rs

@@ -7,6 +7,7 @@
 // except according to those terms.
 
 #![cfg_attr(feature = "unstable", feature(proc_macro, proc_macro_non_items))]
+#![cfg_attr(rustfmt, rustfmt_skip)]
 
 #[cfg_attr(not(feature = "unstable"), macro_use)]
 extern crate indoc;