Update GAE to 1.9.64

Fixes: gh-5422

gradle.properties

@@ -1,3 +1,3 @@
-gaeVersion=1.9.63
+gaeVersion=1.9.64
 springBootVersion=2.0.2.RELEASE
 version=5.1.0.BUILD-SNAPSHOT

gradle/dependency-management.gradle

@@ -45,10 +45,10 @@ dependencyManagement {
 		dependency 'com.fasterxml.jackson.core:jackson-databind:2.9.5'
 		dependency 'com.fasterxml:classmate:1.3.4'
 		dependency 'com.github.stephenc.jcip:jcip-annotations:1.0-1'
-		dependency 'com.google.appengine:appengine-api-1.0-sdk:1.9.63'
-		dependency 'com.google.appengine:appengine-api-labs:1.9.63'
-		dependency 'com.google.appengine:appengine-api-stubs:1.9.63'
-		dependency 'com.google.appengine:appengine-testing:1.9.63'
+		dependency 'com.google.appengine:appengine-api-1.0-sdk:1.9.64'
+		dependency 'com.google.appengine:appengine-api-labs:1.9.64'
+		dependency 'com.google.appengine:appengine-api-stubs:1.9.64'
+		dependency 'com.google.appengine:appengine-testing:1.9.64'
 		dependency 'com.google.appengine:appengine:1.9.63'
 		dependency 'com.google.code.gson:gson:2.8.2'
 		dependency 'com.google.guava:guava:20.0'