Fix temp directory permissions for git fetcher

As reported in zkat#105 `pacote` does
not set permissions on temporary directories for git fetcher when
opts.uid is used to drop privileges (e.g. when using sudo).

This fix passes in the uid and gid to cacache as options. No checking is
required as cacache checks these options before using them.

lib/fetchers/git.js

@@ -157,7 +157,7 @@ function resolve (url, spec, name, opts) {
 function withTmp (opts, cb) {
   if (opts.cache) {
     // cacache has a special facility for working in a tmp dir
-    return cacache.tmp.withTmp(opts.cache, {tmpPrefix: 'git-clone'}, cb)
+    return cacache.tmp.withTmp(opts.cache, {tmpPrefix: 'git-clone', uid: opts.uid, gid: opts.gid}, cb)
   } else {
     const tmpDir = path.join(osenv.tmpdir(), 'pacote-git-tmp')
     const tmpName = uniqueFilename(tmpDir, 'git-clone')