Java 6 Support

Near as I can tell, get-i18n-server v0.21 will only work on JDK 7+. The compiler in the POM is set to support Java 6, but when I attempt to compile on a Java 6 environment, I get:

```
-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running ca.cpp.spike.AppTest
Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.056 sec <<< FAILURE!

Results :

Tests in error:
  testGwtInternationalizationServer(ca.cpp.spike.AppTest): java/lang/ReflectiveOperationException

Tests run: 1, Failures: 0, Errors: 1, Skipped: 0
```

If you'd like this to work with Java 6, then I guess you'll need a new release recompiled to work in v1.6. Alternately, you could just be explicit that it's Java 7+.

Same problem with v0.20. v0.19 seems to work on a quick check.