Update Boot to 1.5.9

Author: Dave Syer

pom.xml

@@ -14,7 +14,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>1.5.8.RELEASE</version>
+        <version>1.5.9.RELEASE</version>
         <relativePath /> <!-- lookup parent from repository -->
     </parent>