Upsizing disk on Flex instances (#425)

diff --git a/app.yaml b/app.yaml
index f512d52..f6b7875 100644
--- a/app.yaml
+++ b/app.yaml
@@ -4,6 +4,7 @@
 resources:
   cpu: 1
   memory_gb: 4
+  disk_size_gb: 20
 
 automatic_scaling:
   min_num_instances: 6