Upgrade to spring 5.1.8

Fixes gh-387

Author: kazuki43zoo

pom.xml

@@ -106,7 +106,7 @@
     <osgi.dynamicImport>*</osgi.dynamicImport>
 
     <mybatis.version>3.5.1</mybatis.version>
-    <spring.version>5.1.6.RELEASE</spring.version>
+    <spring.version>5.1.8.RELEASE</spring.version>
     <spring-batch.version>4.1.2.RELEASE</spring-batch.version>
     <module.name>org.mybatis.spring</module.name>