AsyncMirror and Dropbox fails when there are subfolders with file #276
Description
When using AsyncMirror and Dropbox, and there are subfolders with files, it fails during configure. In the error, it seems to try and fetch but uses the subfolder path twice 
.
I'm running the latest code from the master branch
A simple way to reproduce this error is by using this code in a web page, waiting for it to write the changes, and reload the page.
var dbx = new Dropbox.Dropbox({ fetch, accessToken: 'REDACTED' });
BrowserFS.configure({
fs: "AsyncMirror",
options: {
sync: { fs: "InMemory" },
async: {
fs: "Dropbox",
options: {
client: dbx
}
}
}
}, function (err) {
if (err) { console.log(err); return; }
var fs = BrowserFS.BFSRequire('fs');
if(!fs.existsSync('/subfolder')) {
fs.mkdirSync('/subfolder');
fs.writeFileSync('/subfolder/somefile.txt', 'hello world');
}
});