Replace querystring.unescape with decodeURI

[ghost]

PR Checklist:

• I have run npm test locally and all tests are passing.
• I have added/updated tests for any new behavior.
  
• If this is a significant change, an issue has already been created where the problem / solution was discussed: [N/A, or add link to issue here]
  

PR Description

This addresses (closed) issues #1627 and #1619 which we also hit recently.

Our initial attempts to use couchdb-nano uncovered in this issue, where a URI with basic authorization in it was throwing the error self._qs.unescape is not a function.
This may be due to webpack in our Vue.js environment.

var nano = require('nano')('http://user:password@localhost:5984');
(using nano after this results in request throwing the error

To fix it on our end, I've simply replaced self._qs.unescape with the decodeURI standard javascript call. This now functions correctly in our environment. The issues above mention this issue in Electron builds, which are likely similar to our standard Vue.js (webpack) configuration. As mentioned by @stevage in #1627, I hope this is a benign and fairly straightforward change.

This querystring.unescape call was referenced here:

#475 Use unescape from querystring (@shimaore)

Thanks!

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.