[vimeo] Fix logging in python 3.x

The POST data must be a bytes object.

youtube_dl/extractor/vimeo.py

@@ -17,6 +17,7 @@
     RegexNotFoundError,
     std_headers,
     unsmuggle_url,
+    urlencode_postdata,
 )
 
 
@@ -119,7 +120,8 @@ def _login(self):
         login_url = 'https://vimeo.com/log_in'
         webpage = self._download_webpage(login_url, None, False)
         token = self._search_regex(r'xsrft: \'(.*?)\'', webpage, 'login token')
-        data = compat_urllib_parse.urlencode({'email': username,
+        data = urlencode_postdata({
+            'email': username,
             'password': password,
             'action': 'login',
             'service': 'vimeo',