meta: Fix README CI badge (#401)

Author: Swatinem

README.md

@@ -7,7 +7,7 @@
 
 # Sentry SDK for Rust
 
-[![Build Status](https://travis-ci.com/getsentry/sentry-rust.svg?branch=master)](https://travis-ci.com/getsentry/sentry-rust)
+[![Build Status](https://github.com/getsentry/sentry-rust/workflows/CI/badge.svg)](https://github.com/getsentry/sentry-rust/actions?workflow=CI)
 [![codecov](https://codecov.io/gh/getsentry/sentry-rust/branch/master/graph/badge.svg?token=x4RzFE8N6t)](https://codecov.io/gh/getsentry/sentry-rust)
 
 This workspace contains various crates that provide support for logging events and errors / panics to the