Switched broken pypip.in badges to shields.io

[movermeyer]

Hello, this is an auto-generated Pull Request. (Feedback?)

Some time ago, pypip.in shut down. This broke the badges for a bunch of repositories, including django-terms. Thankfully, an equivalent service is run by shields.io. This pull request changes the badges to use shields.io instead.

Unfortunately, PyPI has removed download statistics from their API, which means that even the shields.io "download count" badges are broken (they display "no longer available". See this). So those badges should really be removed entirely. Since this is an automated process (and trying to automatically remove the badges from READMEs can be tricky), this pull request just replaces the URL with the shields.io syntax.

[coveralls]

Coverage decreased (-20.4%) to 71.66% when pulling e35e4687a2a7cbb92806e351c440609fc1afbcf7 on movermeyer:fix_badges into 2555c2cf5abf14adef9a8e2dd22c4a9076396a10 on BertrandBordage:master.