Enable to export artifacts for zpages and exporters. (#568)

diff --git a/build.gradle b/build.gradle
index b0de9b2..48719a3 100644
--- a/build.gradle
+++ b/build.gradle
@@ -248,6 +248,9 @@
     uploadArchives.onlyIf {
         name in ['opencensus-api',
                  'opencensus-contrib-agent',
+                 'opencensus-contrib-zpages',
+                 'opencensus-exporter-trace-logging',
+                 'opencensus-exporter-trace-stackdriver',
                  'opencensus-impl-core',
                  'opencensus-impl-lite',
                  'opencensus-impl',