Preparing for v0.3.1 release

Changelog.md

+# 0.3.1
+
+ * Added missing __init__.py
 # 0.3.0
 
  * Added support for itemsource interface, allowing s3 hosting

cellxgene_gateway/__init__.py

@@ -7,4 +7,4 @@
 # OR CONDITIONS OF ANY KIND, either express or implied. See the License for
 # the specific language governing permissions and limitations under the License.
 
-__version__ = "0.3.0"
+__version__ = "0.3.1"