docs: fix license link in README (#51)

Signed-off-by: Jan Kowalleck <[email protected]>

Author: jkowalleck

README.md

@@ -2,7 +2,7 @@
 
 [![Gem Version](https://img.shields.io/gem/v/cyclonedx-ruby?logo=rubygems&logoColor=white)](https://rubygems.org/gems/cyclonedx-ruby)
 [![CT status](https://img.shields.io/github/actions/workflow/status/CycloneDX/cyclonedx-ruby-gem/ruby.yml?branch=master&logo=GitHub&logoColor=white)](https://github.com/CycloneDX/cyclonedx-ruby-gem/actions/workflows/ruby.yml?query=branch%3Amaster)
-[![License](https://img.shields.io/badge/license-Apache%202.0-brightgreen.svg)][License]  
+[![License](https://img.shields.io/github/license/CycloneDX/cyclonedx-ruby-gem?logo=open%20source%20initiative&logoColor=white)][license_file]    
 [![Website](https://img.shields.io/badge/https://-cyclonedx.org-blue.svg)](https://cyclonedx.org/)
 [![Slack Invite](https://img.shields.io/badge/Slack-Join-blue?logo=slack&labelColor=393939)](https://cyclonedx.org/slack/invite)
 [![Group Discussion](https://img.shields.io/badge/discussion-groups.io-blue.svg)](https://groups.io/g/CycloneDX)
@@ -61,6 +61,6 @@ Copyright & License
 
 CycloneDX Ruby Gem is Copyright (c) OWASP Foundation. All Rights Reserved.
 
-Permission to modify and redistribute is granted under the terms of the Apache 2.0 license. See the [LICENSE] file for the full license.
+Permission to modify and redistribute is granted under the terms of the Apache 2.0 license. See the [LICENSE][license_file] file for the full license.
 
-[License]: https://github.com/CycloneDX/cyclonedx-ruby-gem/blob/master/LICENSE
+[license_file]: https://github.com/CycloneDX/cyclonedx-ruby-gem/blob/master/LICENSE.txt