Travis CI: Extend the build matric for Scalaz Seven branch

Travis CI has introduced new 64-bit infrastructure for JVM builds:

I got following results:
 * 2.10.0 fails (with both JDK7) when `;compile;test` targets are coupled: https://travis-ci.org/gildegoma/scalaz/builds/4095250
 * the whole build matrix passes when I split `compile` and `test` in two processes: https://travis-ci.org/gildegoma/scalaz/builds/4101184

Is the second way to build a correct practice, or should we tune JVM args, to get the default build style to pass as well ?