AI 149080: Change default PDK app engine version to 2

Automated import of CL 149080
diff --git a/pdk/hosting/app.yaml b/pdk/hosting/app.yaml
index 6e08141..b36efe8 100644
--- a/pdk/hosting/app.yaml
+++ b/pdk/hosting/app.yaml
@@ -1,5 +1,5 @@
 application: pdk-docs
-version: 1
+version: 2
 runtime: python
 api_version: 1