tour: update to the App Engine Go 1.14 runtime

Reference:

•	https://cloud.google.com/appengine/docs/standard/go/runtime

Change-Id: I46b87098ed04c9c5d9f84193c9d72f9d30a59233
Reviewed-on: https://go-review.googlesource.com/c/tour/+/266818
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Alexander Rakoczy <alex@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

app.yaml

diff --git a/app.yaml b/app.yaml
index aab2f02..9de61cf 100644
--- a/app.yaml
+++ b/app.yaml
@@ -1,5 +1,5 @@
 service: tour
-runtime: go112
+runtime: go114
 
 env_variables:
   GOLANGORG_CHECK_COUNTRY: true