work without permissions to create unpacked_bin

From https://github.com/stoeffel/elmi-to-json/issues/20#issuecomment-544173285, the issue seems to be that `$NODE_HOME/` is owned by root, but then the install script (or the wrapper script itself if you install with scripts disabled) can't create a folder there (and also couldn't download or modify files there).

The planned fix is that if it doesn't have write access there then it should fallback to unpacking the binaries to `${XDG_CACHE_HOME:-$HOME/.cache}/-binwrap/`

Start by locating the install script and wrapper script that create or modify the unpacked_bin directory. Check how they handle a non-writable $NODE_HOME/; done means binaries fall back to ${XDG_CACHE_HOME:-$HOME/.cache}/-binwrap/ when that location cannot be written.

Written by the indexing model from the issue text.