src/support/sbt: Don't pass -XX:MaxPermSize to JDK 1.8+
src/support/sbt: Don't pass -XX:MaxPermSize to JDK 1.8+

That option is deprecated in JDK 1.8 and causes a warning message.

Closes #75

jeremiahyan/djinni,PSPDFKit-labs/djinni,jrogers/djinni,pwais/djinni,dropbox/djinni,PSPDFKit-labs/djinni,NachoSoto/djinni,iRobotCorporation/djinni,NachoSoto/djinni,trafi/djinni,mknejp/djinni,mknejp/djinni,trafi/djinni,PSPDFKit-labs/djinni,jeremiahyan/djinni,dropbox/djinni,DEGoodmanWilson/djinni,zaren678/djinni,aijiekj/djinni,ragnraok/djinni,dropbox/djinni,csimmons0/djinni,happybits/djinni,happybits/djinni,dropbox/djinni,Wattpad/djinni,DEGoodmanWilson/djinni,aijiekj/djinni,zaren678/djinni,pwais/djinni,anzihenry/djinni,zaren678/djinni,jeremiahyan/djinni,Wattpad/djinni,ragnraok/djinni,NachoSoto/djinni,pwais/djinni,tobefuturer/djinni,ragnraok/djinni,dropbox/djinni,anzihenry/djinni,happybits/djinni,iRobotCorporation/djinni,aijiekj/djinni,zaren678/djinni,tobefuturer/djinni,ragnraok/djinni,iRobotCorporation/djinni,aijiekj/djinni,PSPDFKit-labs/djinni,mknejp/djinni,jeremiahyan/djinni,mrdomino/djinni,anzihenry/djinni,Wattpad/djinni,tobefuturer/djinni,csimmons0/djinni,DEGoodmanWilson/djinni,pwais/djinni,trafi/djinni,iRobotCorporation/djinni,NachoSoto/djinni,DEGoodmanWilson/djinni,mknejp/djinni,anzihenry/djinni,PSPDFKit-labs/djinni,trafi/djinni,jrogers/djinni,trafi/djinni,Wattpad/djinni,mrdomino/djinni,csimmons0/djinni,happybits/djinni,csimmons0/djinni,happybits/djinni,tobefuturer/djinni,jrogers/djinni,jrogers/djinni,mrdomino/djinni,csimmons0/djinni,mrdomino/djinni