Fix Brussels Build

- Update Spring IO plugin to resolve binary incompatability for tests
- Update Dependency Management Plugin which is required for Spring IO
  plugin update
- Update to Spring Boot 1.5.0.RC1. Necessary because new dependency
  management plugin does not work with Boot 1.4.x

Fixes gh-708

samples/httpsession-redis-json/build.gradle

@@ -1,6 +1,7 @@
 buildscript {
     repositories {
         mavenCentral()
+        maven { url "https://repo.spring.io/milestone" }
     }
     dependencies {
         classpath("org.springframework.boot:spring-boot-gradle-plugin:$springBootVersion")
@@ -22,7 +23,7 @@ ext['spring-security.version'] = springSecurityVersion
 
 dependencies {
     compile project(':spring-session'),
-            "org.springframework.boot:spring-boot-starter-redis",
+            "org.springframework.boot:spring-boot-starter-data-redis",
             "org.springframework.boot:spring-boot-starter-web",
             "org.springframework.boot:spring-boot-starter-thymeleaf",
             "org.springframework.boot:spring-boot-starter-security",