proxy: fix typo

Author: EugeneOne1

proxy/config.go

@@ -60,7 +60,7 @@ type Config struct {
 
 	// PendingRequests is used to mitigate the cache poisoning attacks by
 	// tracking identical requests and returning the same response for them,
-	// peforming a single lookup.  If nil, it will be enabled by default.
+	// performing a single lookup.  If nil, it will be enabled by default.
 	PendingRequests *PendingRequestsConfig
 
 	// BeforeRequestHandler is an optional custom handler called before each DNS