Clarify requirements for building from source

CONTRIBUTING.adoc

@@ -41,7 +41,7 @@ should also work without issue.
 
 === Building from source
 To build the source you will need to install
-http://maven.apache.org/run-maven/index.html[Apache Maven] v3.0 or above.
+http://maven.apache.org/run-maven/index.html[Apache Maven] v3.0.6 or above and JDK 1.7.
 
 ==== Default build
 The project can be built from the root directory using the standard maven command:

README.adoc

@@ -76,7 +76,7 @@ Having trouble with Spring Boot, We'd like to help!
 You don't need to build from source to use Spring Boot (binaries in
 http://repo.spring.io[repo.spring.io], but if you want to try out the latest and greatest,
 Spring Boot can be http://maven.apache.org/run-maven/index.html[built with maven]
-v3.0.5 or above.
+v3.0.5 or above. You also need JDK 1.7 (although Boot applications can run on Java 1.6).
 
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