fix(extract): always extract as current user gid/uid

BREAKING CHANGE: pacote will no longer set ownership of extracted
contents -- uid/gid will *only* be used for the cache and other internal
details.

lib/extract-stream.js

@@ -5,16 +5,21 @@ const path = require('path')
 const pipeline = require('mississippi').pipeline
 const tar = require('tar-fs')
 
+let uid
+let gid
+if (process.platform !== 'win32') {
+  uid = process.getuid()
+  gid = process.getgid()
+}
+
 module.exports = extractStream
 function extractStream (dest, opts) {
   opts = opts || {}
   const sawIgnores = {}
   return pipeline(gunzip(), tar.extract(dest, {
     map: (header) => {
-      if (process.platform !== 'win32') {
-        header.uid = opts.uid == null ? header.uid : opts.uid
-        header.gid = opts.gid == null ? header.gid : opts.gid
-      }
+      if (uid != null) { header.uid = uid }
+      if (gid != null) { header.gid = gid }
       // Note: This mirrors logic in the fs read operations that are
       // employed during tarball creation, in the fstream-npm module.
       // It is duplicated here to handle tarballs that are created