[vk] Use `_form_hidden_inputs` when logging in

youtube_dl/extractor/vk.py

@@ -154,9 +154,7 @@ class VKIE(InfoExtractor):
         login_page = self._download_webpage(
             'https://vk.com', None, 'Downloading login page')
 
-        login_form = dict(re.findall(
-            r'<input\s+type="hidden"\s+name="([^"]+)"\s+(?:id="[^"]+"\s+)?value="([^"]*)"',
-            login_page))
+        login_form = self._form_hidden_inputs(login_page)
 
         login_form.update({
             'email': username.encode('cp1251'),