fix(dev-server): allow file change events to pass through (#3001)

update dev-server to allow changes in directories listed in copy tasks 
of a stencil config file to be updated instantly, rather than having to
restart the server.

STENCIL-29: Feature Request: Ability to watch a copy task source and refresh www build when modified

src/sys/node/node-sys.ts

@@ -430,7 +430,7 @@ export function createNodeSys(c: { process?: any } = {}) {
         const tsFileWatcher = tsSysWatchDirectory(
           p,
           (fileName) => {
-            callback(normalizePath(fileName), null);
+            callback(normalizePath(fileName), 'fileUpdate');
           },
           recursive
         );