fix: use gist tarball url that works for anonymous gists

Also, this saves an extra 302 redirect on every gist tarball request.

Author: isaacs

git-host-info.js

@@ -42,7 +42,7 @@ var gitHosts = module.exports = {
     'httpstemplate': 'git+https://{domain}/{project}.git{#committish}',
     'shortcuttemplate': '{type}:{project}{#committish}',
     'pathtemplate': '{project}{#committish}',
-    'tarballtemplate': 'https://{domain}/{user}/{project}/archive/{committish}.tar.gz',
+    'tarballtemplate': 'https://codeload.github.com/gist/{project}/tar.gz/{committish}',
     'hashformat': function (fragment) {
       return 'file-' + formatHashFragment(fragment)
     }

test/gist.js

@@ -25,7 +25,7 @@ test('fromUrl(gist url)', function (t) {
       t.is(hostinfo.file(''), 'https://gist.githubusercontent.com/111/' + proj + '/raw/' + (branch ? branch + '/' : ''), label + ' -> file')
       t.is(hostinfo.file('C'), 'https://gist.githubusercontent.com/111/' + proj + '/raw/' + (branch ? branch + '/' : '') + 'C', label + ' -> file')
       t.is(hostinfo.file('C/D'), 'https://gist.githubusercontent.com/111/' + proj + '/raw/' + (branch ? branch + '/' : '') + 'C/D', label + ' -> file')
-      t.is(hostinfo.tarball(), 'https://gist.github.com/111/' + proj + '/archive/' + (branch || 'master') + '.tar.gz', label + ' -> tarball')
+      t.is(hostinfo.tarball(), 'https://codeload.github.com/gist/' + proj + '/tar.gz/' + (branch || 'master'), label + ' -> tarball')
     }
   }