Compile samples and integration tests with Java 8

Update the samples and integration tests to use Java 8. There's no
specific reason to keep them on Java 6 and it helps keep Eclipse happy
if we upgrade.

spring-boot-samples/spring-boot-sample-web-static/pom.xml

@@ -17,7 +17,6 @@
 		<url>http://www.spring.io</url>
 	</organization>
 	<properties>
-		<java.version>1.7</java.version>
 		<main.basedir>${basedir}/../..</main.basedir>
 	</properties>
 	<dependencies>