Do not try to format deleted files

Reviewed By: jvillard

Differential Revision: D9295716

fbshipit-source-id: 6333d8e01

Makefile

@@ -145,7 +145,7 @@ OCAMLFORMAT_EXE?=ocamlformat
 
 .PHONY: fmt
 fmt:
-	parallel $(OCAMLFORMAT_EXE) -i ::: $$(git diff --name-only $$(git merge-base origin/master HEAD) | grep "\.mli\?$$")
+	parallel $(OCAMLFORMAT_EXE) -i ::: $$(git diff --name-only --diff-filter=ACMRU $$(git merge-base origin/master HEAD) | grep "\.mli\?$$")
 
 DUNE_ML:=$(shell find * -name 'dune*.in' | grep -v workspace | grep -v sledge)