Upgrade to Spring Boot 1.5.20

Fixes gh-312

Author: kazuki43zoo

pom.xml

@@ -69,7 +69,7 @@
   <properties>
     <mybatis.version>3.4.6</mybatis.version>
     <mybatis-spring.version>1.3.2</mybatis-spring.version>
-    <spring-boot.version>1.5.19.RELEASE</spring-boot.version>
+    <spring-boot.version>1.5.20.RELEASE</spring-boot.version>
   </properties>
 
   <dependencyManagement>