Bumped version to 3.9.0a1 (#266)

diff --git a/pulsar/__about__.py b/pulsar/__about__.py
index a3a2fb5..9be5048 100644
--- a/pulsar/__about__.py
+++ b/pulsar/__about__.py
@@ -16,4 +16,4 @@
 # specific language governing permissions and limitations
 # under the License.
 #
-__version__='3.8.0a1'
+__version__='3.9.0a1'