Updated build shield URL

Author: arjanz

README.md

@@ -1,6 +1,6 @@
 # Python SCALE Codec
 
-[![Build Status](https://img.shields.io/github/workflow/status/polkascan/py-scale-codec/Run%20unit%20tests)](https://github.com/polkascan/py-scale-codec/actions?query=workflow%3A%22Run+unit+tests%22)
+[![Build Status](https://img.shields.io/github/actions/workflow/status/polkascan/py-scale-codec/unittests.yml?branch=master)](https://github.com/polkascan/py-scale-codec/actions/workflows/unittests.yml?query=workflow%3A%22Run+unit+tests%22)
 [![Latest Version](https://img.shields.io/pypi/v/scalecodec.svg)](https://pypi.org/project/scalecodec/) 
 [![Supported Python versions](https://img.shields.io/pypi/pyversions/scalecodec.svg)](https://pypi.org/project/scalecodec/)
 [![License](https://img.shields.io/pypi/l/scalecodec.svg)](https://github.com/polkascan/py-scale-codec/blob/master/LICENSE)