fix #23 - fix example oauth2_client.pl

which was breaking due to the fix_get_token hack, which itself has been
remove from Mojolicious::Plugin::OAuth2

[1] e1da641f1d21b8136d5d27d46c542d995f02367b in
https://github.com/marcusramberg/Mojolicious-Plugin-OAuth2 # which was
ages ago so am surprised this wasn't reported sooner

examples/oauth2_client.pl

@@ -8,7 +8,6 @@
 my $host = $ENV{HOST} // '127.0.0.1';
 
 plugin 'OAuth2', {
-  fix_get_token => 1,
   overly_attached_social_network => {
      authorize_url => "https://$host:3000/oauth/authorize?response_type=code",
      token_url     => "https://$host:3000/oauth/access_token",