Use java8 for osx builds. (#1598)
Use java8 for osx builds. (#1598)


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