fix: no brackets with single operators (bug #273)
fix: no brackets with single operators (bug #273)

* Use brackets after unary minus followed by an OperatorNode with + or -
 - "-(a+b)", "-(a-b)"
* Use brackets in fron of postfix operators like '!' (for OperatorNode)
 - "(a*b)!", "(a+b)!"

saromanov/mathjs,javiercejudo/mathjs,mefozzy/mathjs,FSMaxB/mathjs,FSMaxB/mathjs,FSMaxB/mathjs,javiercejudo/mathjs,mikberg/mathjs,jomachim/mathjs,FSMaxB/mathjs,josdejong/mathjs,tomekwi/mathjs,ericman314/mathjs,rjbaucells/mathjs,devanp92/mathjs,josdejong/mathjs,tomekwi/mathjs,josdejong/mathjs,luke-gumbley/mathjs,DenisGorbachev/mathjs,golmansax/mathjs,mcanthony/mathjs,saromanov/mathjs,FSMaxB/mathjs,josdejong/mathjs,frbl/mathjs,luke-gumbley/mathjs,frbl/mathjs,golmansax/mathjs,DenisGorbachev/mathjs,mikberg/mathjs,devanp92/mathjs,rjbaucells/mathjs,mcanthony/mathjs,ericman314/mathjs,jomachim/mathjs,josdejong/mathjs,mefozzy/mathjs