Add opencensus-contrib-log-correlation-log4j2 to the list of released artifacts. (#1415)

This commit also updates the changelog.
diff --git a/build.gradle b/build.gradle
index e0d9938..7b237ab 100644
--- a/build.gradle
+++ b/build.gradle
@@ -418,10 +418,7 @@
                  'opencensus-contrib-grpc-metrics',
                  'opencensus-contrib-grpc-util',
                  'opencensus-contrib-http-util',
-
-                 // TODO(sebright): Uncomment opencensus-contrib-log-correlation-log4j when it is complete.
-                 // 'opencensus-contrib-log-correlation-log4j',
-
+                 'opencensus-contrib-log-correlation-log4j2',
                  'opencensus-contrib-log-correlation-stackdriver',
                  'opencensus-contrib-monitored-resource-util',
                  'opencensus-contrib-spring',