Update comments

src/compiler/sys.ts

@@ -398,8 +398,8 @@ namespace ts {
                     // and https://github.com/Microsoft/TypeScript/issues/4643), therefore
                     // if the current node.js version is newer than 4, use `fs.watch` instead.
                     if (isNode4OrLater()) {
-                        // Note: in node the callback of fs.watch is given only the base file name as a parameter
-                        return _fs.watch(fileName, (eventName: string, baseFileName: string) => callback(fileName));
+                        // Note: in node the callback of fs.watch is given only the relative file name as a parameter
+                        return _fs.watch(fileName, (eventName: string, relativeFileName: string) => callback(fileName));
                     }
 
                     var watchedFile = watchedFileSet.addFile(fileName, callback);