Madhavan

[bug/qa] Fix lint errors being ignored #485

1

## Checklist - [x] I have read the [OpenWISP Contributing Guidelines](http://openwisp.io/docs/developer/contributing.html). - [x] I have manually tested the changes proposed in this pull request. - [x] I have written new...

## Checklist - [x] I have read the [OpenWISP Contributing Guidelines](http://openwisp.io/docs/developer/contributing.html). - [x] I have manually tested the changes proposed in this pull request. - [x] I have written new...

Replace third-party JSONField with Django's built-in JSONField

1

## Checklist - [x] I have read the [OpenWISP Contributing Guidelines](http://openwisp.io/docs/developer/contributing.html). - [x] I have manually tested the changes proposed in this pull request. - [x] I have written new...

## Checklist - [x] I have read the [OpenWISP Contributing Guidelines](http://openwisp.io/docs/developer/contributing.html). - [x] I have manually tested the changes proposed in this pull request. - [ ] I have written...