Update Changelog for release

Author: jleopold28

CHANGELOG.md

@@ -1,4 +1,7 @@
 # Unreleased
+
+# v5.19
+
 - [Issue #422](https://github.com/manheim/terraform-pipeline/issues/422) TerraformPlugin and TerraformPluginVersion should implement TerraformInitCommandPlugin
 - [Issue #379](https://github.com/manheim/terraform-pipeline/issues/379) Support Terraform 0.15. Added `-chdir` argument.
 - [Issue #395](https://github.com/manheim/terraform-pipeline/issues/395) Support Terraform 1.0. Added `-chdir` argument.