Adds support for promoting to maven central (#78)

* Adds support for promoting to maven central

scripts/Dockerfile

@@ -1,6 +1,8 @@
 ARG base_image=ubuntu:bionic
 FROM ${base_image}
 
+ADD https://repo.spring.io/libs-release/io/spring/concourse/releasescripts/concourse-release-scripts/0.3.2/concourse-release-scripts-0.3.2.jar /opt/concourse-release-scripts.jar
+
 RUN apt-get update && apt-get install --no-install-recommends -y \
-    git \
+    git gnupg \
  && rm -rf /var/lib/apt/lists/*