Use dartsim in homebrew-core instead of dartsim/dart/dartsim6 (#378)
Use dartsim in homebrew-core instead of dartsim/dart/dartsim6 (#378)

* Use dartsim in homebrew-core

* make dartsim recommended instead of optional

* bump revision

* gazebo9 9.0.0_2 el_capitan bottle

* gazebo9 9.0.0_2 sierra bottle

* gazebo9 9.0.0_2 high_sierra bottle

scpeters/homebrew-simulation,j-rivero/homebrew-simulation,osrf/homebrew-simulation