Bump the Option::replace stabilize version to 1.31.0

src/libcore/option.rs

@@ -878,7 +878,7 @@ impl<T> Option<T> {
  /// assert_eq!(old, None);
  /// ```
  #[inline]
- #[stable(feature = "option_replace", since = "1.30.0")]
+ #[stable(feature = "option_replace", since = "1.31.0")]
  pub fn replace(&mut self, value: T) -> Option<T> {
  mem::replace(self, Some(value))
  }