Use gitbase v0.19.0-beta3 in staging

Signed-off-by: Carlos Martín <carlos.martin.sanchez@gmail.com>

Author: carlosms

.helm-defaults.yml

@@ -51,7 +51,7 @@ gitbaseServer:
       url: https://github.com/src-d/siva-java.git
   image:
     repository: srcd/gitbase
-    tag: v0.18.0
+    tag: v0.19.0-beta3
     pullPolicy: IfNotPresent
   squashEnable: "true"
   readonly: "true"