gmsh 2.13.2
gmsh 2.13.2

* opencascade is now optional since it does not compile on Sierra

Closes #4404.

Signed-off-by: Jonathan Chang <0bd51b8a224feeddb634965eebae512adcd49a8d@gmail.com>

parcollet/homebrew-science,maplesond/homebrew-science,DabeDotCom/homebrew-science,heuermh/homebrew-science,kozo2/homebrew-science,quantumsteve/homebrew-science,andrewjpage/homebrew-science,pditommaso/homebrew-science,philippbayer/homebrew-science,dpo/homebrew-science