Fix #132: Python 2 getheaders should be Python 3 get_all

Author: jyapayne

command_line.py

@@ -1257,7 +1257,7 @@ def download_file(self, path, setting):
         web_file = request.urlopen(url)
         f = open(tmp_file, 'ab')
         meta = web_file.info()
-        file_size = tmp_size + int(meta.getheaders("Content-Length")[0])
+        file_size = tmp_size + int(meta.get_all("Content-Length")[0])
 
         version = self.selected_version()
         version_file = self.settings['base_url'].format(version)