transtive_relation: fix typo in comment for `parents`

src/librustc_data_structures/transitive_relation.rs

@@ -303,7 +303,7 @@ pub fn minimal_upper_bounds(&self, a: &T, b: &T) -> Vec<&T> {
     /// Given an element A, returns the maximal set {B} of elements B
     /// such that
     ///
-    /// - A != A
+    /// - A != B
     /// - A R B is true
     /// - for each i, j: B[i] R B[j] does not hold
     ///