Java 7 version?

I'm building on travis using openjdk7 and I'm getting Caused by: java.lang.UnsupportedClassVersionError: io/krakens/grok/api/GrokCompiler : Unsupported major.minor version 52.0.

I see there's a lot of "lambda-style" code in 0.1.9, is there any plan on backporting to java7?