Upgrade to spring-framework 5.2.1 on Travis CI

Fixes gh-418

Author: kazuki43zoo

.travis.yml

@@ -9,7 +9,7 @@ jdk:
 
 script:
   - ./mvnw clean verify
-  - ./mvnw clean verify -Dspring.version=5.2.0.RELEASE -Dspring-batch.version=4.2.0.RELEASE -Denforcer.fail=false
+  - ./mvnw clean verify -Dspring.version=5.2.1.RELEASE -Dspring-batch.version=4.2.0.RELEASE -Denforcer.fail=false
 
 after_success:
   - chmod -R 777 ./travis/after_success.sh