storage: add copyDir

we changed listDir in c44863a9bb to list
a directory . this broke copy for files since a '/' is added when listing
the file.

src/storage/interface.js

@@ -20,6 +20,7 @@ exports = module.exports = {
 
     download,
     copy,
+    copyDir,
 
     listDir,
 
@@ -94,6 +95,15 @@ async function copy(apiConfig, oldFilePath, newFilePath, progressCallback) {
     throw new BoxError(BoxError.NOT_IMPLEMENTED, 'copy is not implemented');
 }
 
+async function copyDir(apiConfig, oldFilePath, newFilePath, progressCallback) {
+    assert.strictEqual(typeof apiConfig, 'object');
+    assert.strictEqual(typeof oldFilePath, 'string');
+    assert.strictEqual(typeof newFilePath, 'string');
+    assert.strictEqual(typeof progressCallback, 'function');
+
+    throw new BoxError(BoxError.NOT_IMPLEMENTED, 'copy is not implemented');
+}
+
 async function listDir(apiConfig, dir, batchSize, marker) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert.strictEqual(typeof dir, 'string');