Update PriorityQueue`2.xml

Author: eiriktsarpalis

xml/System.Collections.Generic/PriorityQueue`2.xml

@@ -26,7 +26,7 @@
 
 ## Remarks
 
-Implements an array-backed, quaternary min-heap. Each element is enqueued with an associated priority that determines the dequeue order. Elements with the lowest priority are dequeued first. Note that the type does not guarantee first-in-first-out semantics.
+Implements an array-backed, quaternary min-heap. Each element is enqueued with an associated priority that determines the dequeue order. Elements with the lowest priority are dequeued first. Note that the type does not guarantee first-in-first-out semantics for elements of equal priority.
 
       ]]></format>
     </remarks>