Sign parent pom upon release
Sign parent pom upon release

Maven Central requires all uploaded artifacts to be signed. So we also
need to sign the parent pom.

Change-Id: I38227a9f4ca47b89c13e4609e41eedcbdc09b60e

mackerl/jacoco-toolbox,quelltextlich/jacoco-toolbox,quelltextlich/jacoco-toolbox,mackerl/jacoco-toolbox