Make checkProxyURL use its argument.
Make checkProxyURL use its argument.

It was using the same global variable as was passed as the argument, so
the behavior was still correct.

wyuelin/mymeek,projectarkc/meek,wyuelin/mymeek,infinity0/meek,wyuelin/mymeek,projectarkc/meek,infinity0/meek,gorshell/forkmeek,Yawning/meek,infinity0/meek,gorshell/forkmeek,Yawning/meek,gorshell/forkmeek,Yawning/meek,projectarkc/meek,projectarkc/meek,wyuelin/mymeek,infinity0/meek,Yawning/meek,infinity0/meek,gorshell/forkmeek,projectarkc/meek