doc: fix busted doctest, r=burningtree.

graydon · graydon · commit bbc04dbb244d · 2012-12-07T14:40:56.000-08:00
diff --git a/doc/rust.md b/doc/rust.md
@@ -2710,7 +2710,7 @@ trait Printable {
 }
 
 impl ~str: Printable {
-  fn to_str() -> ~str { self }
+  fn to_str() -> ~str { copy self }
 }
 ~~~~~~
 
