Fix bashism in Makefile
Fix bashism in Makefile

rgrinberg/merlin,ocaml/merlin,haselwarter/merlin,dra27/merlin,rgrinberg/merlin,chambart/merlin,ocaml/merlin,chambart/merlin,rgrinberg/merlin,neojski/merlin,dra27/merlin,chriskonstad/merlin,fxfactorial/merlin,chriskonstad/merlin,rgrinberg/merlin,fxfactorial/merlin,neojski/merlin,ocaml/merlin,fxfactorial/merlin,chambart/merlin,the-lambda-church/merlin,the-lambda-church/merlin,the-lambda-church/merlin,haselwarter/merlin,chambart/merlin,haselwarter/merlin,haselwarter/merlin,neojski/merlin,ocaml/merlin,dra27/merlin,dra27/merlin,fxfactorial/merlin,neojski/merlin