[Common] Fix creation of pidfile via command option

Python 3 raises a TypeError for binary file mode and writing text string.

Fixes: #3278

deluge/argparserbase.py

@@ -325,7 +325,7 @@ def _handle_ui_options(self, options):
 
             # Write pid file before chuid
             if options.pidfile:
-                with open(options.pidfile, 'wb') as _file:
+                with open(options.pidfile, 'w') as _file:
                     _file.write('%d\n' % os.getpid())
 
             if not common.windows_check():