Replace CI badge

Author: sh-cho

README.md

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 # Tolerant PHP Parser
-[![Build Status](https://travis-ci.org/Microsoft/tolerant-php-parser.svg?branch=master)](https://travis-ci.org/Microsoft/tolerant-php-parser)
+[![CI](https://github.com/microsoft/tolerant-php-parser/actions/workflows/main.yml/badge.svg?branch=main)](https://github.com/microsoft/tolerant-php-parser/actions/workflows/main.yml)
 
 This is an early-stage PHP parser designed, from the beginning, for IDE usage scenarios (see [Design Goals](#design-goals) for more details). There is
 still a ton of work to be done, so at this point, this repo mostly serves as