Declare the GitHub repo as the place to report issues

[briandfoy]

As noted in #189, this distro's "Issues" link in MetaCPAN points to RT. To fix this, you can add the bugtracker in the metadata in Makefile.PL:

(META_ADD => {
                             'meta-spec' => { version => 2 },
                             resources => {
                                 repository => {
                                     type => 'git',
                                     url => 'https://github.com/andk/cpanpm'
                                 },
		        	bugtracker => {
				    web    => "https://github.com/andk/cpanpm/issues",
				},
                             },
    

Likewise, you'd have to update the README.

Or, alternately, if you want issues reported to RT, which is a hair's breadth from shutting down, I suggest that you turn off GitHub issues.