fix: Update deprecated constant usage (#885)

Author: mykola-mokhnach

lib/helpers.js

@@ -7,7 +7,7 @@ import { fs, system } from 'appium/support';
  */
 export async function isWriteable(filePath) {
   try {
-    await fs.access(filePath, fs.W_OK);
+    await fs.access(filePath, fs.constants.W_OK);
     if (system.isWindows()) {
       // On operating systems, where access-control policies may
       // limit access to the file system, `fs.access` does not work