Fix PrunedLiveness comment typo

Author: atrick

include/swift/SIL/PrunedLiveness.h

@@ -705,7 +705,7 @@ class PrunedLiveRange : public PrunedLiveness {
   /// Precondition: \p liveness.getDiscoveredBlocks() is a valid list of all
   /// live blocks with no duplicates.
   ///
-  /// The computed boundary will completely post-dominate, including dead end
+  /// The computed boundary will completely post-dominated, including dead end
   /// paths. The client should query DeadEndBlocks to ignore those dead end
   /// paths.
   void computeBoundary(PrunedLivenessBoundary &boundary) const;