Modernize shields.

This references the GitHub workflows, and eliminates the goreportcard
which appears to be defunct now.

README.md

@@ -4,14 +4,12 @@
 _Tcell_ is a _Go_ package that provides a cell based view for text terminals, like _XTerm_.
 It was inspired by _termbox_, but includes many additional improvements.
 
-[![Linux Status](https://img.shields.io/travis/gdamore/tcell.svg?label=linux)](https://travis-ci.org/gdamore/tcell)
-[![Windows Status](https://img.shields.io/appveyor/ci/gdamore/tcell.svg?label=windows)](https://ci.appveyor.com/project/gdamore/tcell)
-[![Apache License](https://img.shields.io/badge/license-APACHE2-blue.svg)](https://github.com/gdamore/tcell/blob/master/LICENSE)
-[![Documentation](https://img.shields.io/badge/godoc-reference-blue.svg)](https://pkg.go.dev/github.com/gdamore/tcell/v2)
-[![Report Card](https://goreportcard.com/badge/gdamore/tcell)](http://goreportcard.com/report/gdamore/tcell/v2)
-[![Discord](https://img.shields.io/discord/639503822733180969?label=discord)](https://discord.gg/urTTxDN)
-[![Coverage](https://codecov.io/gh/gdamore/tcell/branch/master/graph/badge.svg)](https://codecov.io/gh/gdamore/tcell)
-
+[![Linux](https://img.shields.io/github/workflow/status/gdamore/tcell/linux?logoColor=grey&logo=linux&label=)](https://github.com/gdamore/tcell/actions/workflows/linux.yml)
+[![Windows](https://img.shields.io/github/workflow/status/gdamore/tcell/windows?logoColor=grey&logo=windows&label=)](https://github.com/gdamore/tcell/actions/workflows/windows.yml)
+[![Apache License](https://img.shields.io/github/license/gdamore/tcell.svg?logoColor=silver&logo=opensourceinitiative&color=blue&label=)](https://github.com/gdamore/tcell/blob/master/LICENSE)
+[![Docs](https://img.shields.io/badge/godoc-reference-blue.svg?label=&logo=go)](https://pkg.go.dev/github.com/gdamore/tcell/v2)
+[![Discord](https://img.shields.io/discord/639503822733180969?label=&logo=discord)](https://discord.gg/urTTxDN)
+[![Coverage](https://img.shields.io/codecov/c/github/gdamore/tcell?logoColor=grey&logo=codecov&label=)](https://codecov.io/gh/gdamore/tcell)
 
 NOTE: This is version 2 of _Tcell_.  There are breaking changes relative to version 1.
 Version 1.x remains available using the import `github.com/gdamore/tcell`.