README.md: update badges

* remove .svg from shields.io badges since it's the default
* switch to shields.io for the OC badges too
* fix badgesize badges' labels

README.md

@@ -55,19 +55,19 @@ Read the [Getting started page](https://getbootstrap.com/docs/4.5/getting-starte
 
 [![Slack](https://bootstrap-slack.herokuapp.com/badge.svg)](https://bootstrap-slack.herokuapp.com/)
 [![Build Status](https://github.com/twbs/bootstrap/workflows/JS%20Tests/badge.svg?branch=v4-dev)](https://github.com/twbs/bootstrap/actions?query=workflow%3AJS+Tests+branch%3Av4-dev)
-[![npm version](https://img.shields.io/npm/v/bootstrap.svg)](https://www.npmjs.com/package/bootstrap)
-[![Gem version](https://img.shields.io/gem/v/bootstrap.svg)](https://rubygems.org/gems/bootstrap)
-[![Meteor Atmosphere](https://img.shields.io/badge/meteor-twbs%3Abootstrap-blue.svg)](https://atmospherejs.com/twbs/bootstrap)
-[![Packagist Prerelease](https://img.shields.io/packagist/vpre/twbs/bootstrap.svg)](https://packagist.org/packages/twbs/bootstrap)
-[![NuGet](https://img.shields.io/nuget/vpre/bootstrap.svg)](https://www.nuget.org/packages/bootstrap/absoluteLatest)
-[![peerDependencies Status](https://img.shields.io/david/peer/twbs/bootstrap.svg)](https://david-dm.org/twbs/bootstrap?type=peer)
-[![devDependency Status](https://img.shields.io/david/dev/twbs/bootstrap.svg)](https://david-dm.org/twbs/bootstrap?type=dev)
-[![Coverage Status](https://img.shields.io/coveralls/github/twbs/bootstrap/v4-dev.svg)](https://coveralls.io/github/twbs/bootstrap?branch=v4-dev)
-[![CSS gzip size](https://img.badgesize.io/twbs/bootstrap/v4-dev/dist/css/bootstrap.min.css?compression=gzip&label=CSS+gzip+size)](https://github.com/twbs/bootstrap/tree/v4-dev/dist/css/bootstrap.min.css)
-[![JS gzip size](https://img.badgesize.io/twbs/bootstrap/v4-dev/dist/js/bootstrap.min.js?compression=gzip&label=JS+gzip+size)](https://github.com/twbs/bootstrap/tree/v4-dev/dist/js/bootstrap.min.js)
+[![npm version](https://img.shields.io/npm/v/bootstrap)](https://www.npmjs.com/package/bootstrap)
+[![Gem version](https://img.shields.io/gem/v/bootstrap)](https://rubygems.org/gems/bootstrap)
+[![Meteor Atmosphere](https://img.shields.io/badge/meteor-twbs%3Abootstrap-blue)](https://atmospherejs.com/twbs/bootstrap)
+[![Packagist Prerelease](https://img.shields.io/packagist/vpre/twbs/bootstrap)](https://packagist.org/packages/twbs/bootstrap)
+[![NuGet](https://img.shields.io/nuget/vpre/bootstrap)](https://www.nuget.org/packages/bootstrap/absoluteLatest)
+[![peerDependencies Status](https://img.shields.io/david/peer/twbs/bootstrap)](https://david-dm.org/twbs/bootstrap?type=peer)
+[![devDependency Status](https://img.shields.io/david/dev/twbs/bootstrap)](https://david-dm.org/twbs/bootstrap?type=dev)
+[![Coverage Status](https://img.shields.io/coveralls/github/twbs/bootstrap/v4-dev)](https://coveralls.io/github/twbs/bootstrap?branch=v4-dev)
+[![CSS gzip size](https://img.badgesize.io/twbs/bootstrap/v4-dev/dist/css/bootstrap.min.css?compression=gzip&label=CSS%20gzip%20size)](https://github.com/twbs/bootstrap/tree/v4-dev/dist/css/bootstrap.min.css)
+[![JS gzip size](https://img.badgesize.io/twbs/bootstrap/v4-dev/dist/js/bootstrap.min.js?compression=gzip&label=JS%20gzip%20size)](https://github.com/twbs/bootstrap/tree/v4-dev/dist/js/bootstrap.min.js)
 [![BrowserStack Status](https://www.browserstack.com/automate/badge.svg?badge_key=SkxZcStBeExEdVJqQ2hWYnlWckpkNmNEY213SFp6WHFETWk2bGFuY3pCbz0tLXhqbHJsVlZhQnRBdEpod3NLSDMzaHc9PQ==--3d0b75245708616eb93113221beece33e680b229)](https://www.browserstack.com/automate/public-build/SkxZcStBeExEdVJqQ2hWYnlWckpkNmNEY213SFp6WHFETWk2bGFuY3pCbz0tLXhqbHJsVlZhQnRBdEpod3NLSDMzaHc9PQ==--3d0b75245708616eb93113221beece33e680b229)
-[![Backers on Open Collective](https://opencollective.com/bootstrap/backers/badge.svg)](#backers)
-[![Sponsors on Open Collective](https://opencollective.com/bootstrap/sponsors/badge.svg)](#sponsors)
+[![Backers on Open Collective](https://img.shields.io/opencollective/backers/bootstrap)](#backers)
+[![Sponsors on Open Collective](https://img.shields.io/opencollective/sponsors/bootstrap)](#sponsors)
 
 
 ## What's included