docs: README.md: use shields.io for all badges (#237)

Author: XhmikosR

README.md

@@ -2,9 +2,9 @@
 > A super simple site crawler and broken link checker.
 
 [![npm version](https://img.shields.io/npm/v/linkinator.svg)](https://www.npmjs.org/package/linkinator)
-[![Build Status](https://github.com/JustinBeckwith/linkinator/workflows/ci/badge.svg)](https://github.com/JustinBeckwith/linkinator/actions)
-[![codecov](https://codecov.io/gh/JustinBeckwith/linkinator/branch/master/graph/badge.svg)](https://codecov.io/gh/JustinBeckwith/linkinator)
-[![Known Vulnerabilities](https://snyk.io/test/github/JustinBeckwith/linkinator/badge.svg)](https://snyk.io/test/github/JustinBeckwith/linkinator)
+[![Build Status](https://img.shields.io/github/workflow/status/JustinBeckwith/linkinator/ci/master)](https://github.com/JustinBeckwith/linkinator/actions?query=branch%3Amaster+workflow%3Aci)
+[![codecov](https://img.shields.io/codecov/c/github/JustinBeckwith/linkinator/master)](https://codecov.io/gh/JustinBeckwith/linkinator)
+[![Known Vulnerabilities](https://img.shields.io/snyk/vulnerabilities/github/JustinBeckwith/linkinator)](https://snyk.io/test/github/JustinBeckwith/linkinator)
 [![Code Style: Google](https://img.shields.io/badge/code%20style-google-blueviolet.svg)](https://github.com/google/gts)
 [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release)