Fix: make sure all extracted tarballs are r/w enabled

**Summary**

Fixes: #992. This issue was supposed to be fixed by #2826 but it
was not setting directory permissions wide enough. This patch uses
the `readable` and `writable` options provided by the `tar-fs`
package which essentially sets everything to `0o777`.

**Test plan**

N/A

Author: BYK

src/fetchers/tarball-fetcher.js

@@ -67,8 +67,9 @@ export default class TarballFetcher extends BaseFetcher {
     const extractorStream = gunzip();
     const untarStream = tarFs.extract(this.dest, {
       strip: 1,
-      dmode: 0o555, // all dirs should be readable
-      fmode: 0o444, // all files should be readable
+      // everything should be readable and writeable
+      readable: true,
+      writable: true,
       chown: false, // don't chown. just leave as it is
     });