Add the Gradle Versions plugin. (#524)
Add the Gradle Versions plugin. (#524)

* Add the Gradle Versions plugin, https://github.com/ben-manes/gradle-versions-plugin.

* Apply the versions plugin only at the root, making it less spammy.

sebright/instrumentation-java,bogdandrutu/instrumentation-java,songy23/instrumentation-java,songy23/instrumentation-java,bogdandrutu/opencensus-java,sebright/opencensus-java,bogdandrutu/instrumentation-java,sebright/opencensus-java,sebright/instrumentation-java,census-instrumentation/opencensus-java,bogdandrutu/opencensus-java,bogdandrutu/opencensus-java,census-instrumentation/opencensus-java,sebright/opencensus-java,census-instrumentation/opencensus-java,songy23/instrumentation-java