update the since field to 1.12.0 for String AddAssign

diff --git a/src/libcollections/string.rs b/src/libcollections/string.rs
index 688f057604251056b4dd656f138a128f620e1577..3920b57962c872829f3003521bf84d37cb8face6 100644 (file)
--- a/src/libcollections/string.rs
+++ b/src/libcollections/string.rs
@@ -1559,7 +1559,7 @@ fn add(mut self, other: &str) -> String {
     }
 }
 
-#[stable(feature = "rust1", since = "1.11.0")]
+#[stable(feature = "rust1", since = "1.12.0")]
 impl<'a> AddAssign<&'a str> for String {
     #[inline]
     fn add_assign(&mut self, other: &str) {