Bump spring-core, spring-security-config, and spring-boot to the latest version to address security vulnerabilities reported by the latest dependency check

Author: sapessi

aws-serverless-java-container-spring/pom.xml

@@ -16,9 +16,9 @@
     </parent>
 
     <properties>
-        <spring.version>5.1.1.RELEASE</spring.version>
-        <springboot.version>1.5.17.RELEASE</springboot.version>
-        <spring-security.version>5.1.1.RELEASE</spring-security.version>
+        <spring.version>5.1.8.RELEASE</spring.version>
+        <springboot.version>1.5.21.RELEASE</springboot.version>
+        <spring-security.version>5.1.5.RELEASE</spring-security.version>
         <jackson.version>2.9.9</jackson.version>
     </properties>