MakefileExample: Fix AVR_TOOLS_DIR default
MakefileExample: Fix AVR_TOOLS_DIR default

Judging by the default for OS X directly above it and the fact that the current default doesn't work, it seems this should not include the `/bin`.
joshsamuelson/Arduino-Makefile,joshsamuelson/Arduino-Makefile,drpjk/Arduino-Makefile,kindsenior/Arduino-Makefile,exmachina-dev/Arduino-Makefile,WeAreLeka/Arduino-Makefile,theicfire/Arduino-Makefile,WeAreLeka/Arduino-Makefile,AlexSatrapa/Arduino-Makefile,thomaskilian/Arduino-Makefile,drpjk/Arduino-Makefile,sudar/Arduino-Makefile,theicfire/Arduino-Makefile,jamesrob4/Arduino-Makefile,marioaugustorama/Arduino-Makefile,AlexSatrapa/Arduino-Makefile,drpjk/Arduino-Makefile,jamesrob4/Arduino-Makefile,WeAreLeka/Arduino-Makefile,thomaskilian/Arduino-Makefile,tuna-f1sh/Arduino-Makefile,exmachina-dev/Arduino-Makefile,kindsenior/Arduino-Makefile,tuna-f1sh/Arduino-Makefile,sej7278/Arduino-Makefile,marioaugustorama/Arduino-Makefile,sudar/Arduino-Makefile,sej7278/Arduino-Makefile