Fix comment in Algorithms prototype

Author: Dave Abrahams

test/Prototypes/Algorithms.swift.gyb

@@ -678,7 +678,7 @@ extension LazyCollectionProtocol
 
 extension Collection {
     /// Returns the index of the first element in the collection
-    /// that doesn't match the predicate.
+    /// that matches the predicate.
     ///
     /// The collection must already be partitioned according to the
     /// predicate, as if `self.partition(by: predicate)` had already