更新覆盖率标徽

README.md

@@ -2,7 +2,7 @@
 
 [![Build Status](https://github.com/wa-lang/wa/actions/workflows/wa.yml/badge.svg)](https://github.com/wa-lang/wa/actions/workflows/wa.yml)
 [![Go Report Card](https://goreportcard.com/badge/github.com/wa-lang/wa)](https://goreportcard.com/report/github.com/wa-lang/wa)
-[![Coverage Status](https://codecov.io/gh/wa-lang/wa/branch/main/graph/badge.svg)](https://codecov.io/gh/wa-lang/wa)
+[![Coverage Status](https://coveralls.io/repos/github/wa-lang/wa/badge.svg)](https://coveralls.io/github/wa-lang/wa)
 [![GitHub release](https://img.shields.io/github/v/tag/wa-lang/wa.svg?label=release)](https://github.com/wa-lang/wa/releases)
 
 凹语言™（凹读音“Wa”）是[柴树杉](https://github.com/chai2010)、[丁尔男](https://github.com/3dgen)和[史斌](https://github.com/benshi001)设计的实验性编程语言。