chore: fix build status shield in README (#293)

Author: crepererum

README.md

@@ -1,6 +1,6 @@
 # RSKafka
 
-[![CircleCI](https://circleci.com/gh/influxdata/rskafka/tree/main.svg?style=shield&circle-token=531ba1f38035a10da6dbf7cc71e6f55eff496c70)](https://circleci.com/gh/influxdata/rskafka/tree/main)
+[![CircleCI](https://img.shields.io/circleci/build/gh/influxdata/rskafka/main)](https://circleci.com/gh/influxdata/rskafka/tree/main)
 [![Crates.io](https://img.shields.io/crates/v/rskafka)](https://crates.io/crates/rskafka)
 [![Documentation](https://img.shields.io/docsrs/rskafka)](https://docs.rs/crate/rskafka/latest)
 [![License](https://img.shields.io/crates/l/rskafka)](#license)