fix quoting in julia.bat

The command line parser used to be tolerant of this oddity, since the first argument is supposed to use different escaping rules than the other arguments. But now we are using the same rules for all arguments, so it no longer worked.

Makefile

@@ -48,7 +48,7 @@ $(BUILDROOT)/doc/_build/html/en/index.html: $(shell find $(BUILDROOT)/base $(BUI
 
 julia-symlink: julia-cli-$(JULIA_BUILD_MODE)
 ifeq ($(OS),WINNT)
-	@echo '@"%~dp0"\'"$$(echo $(call rel_path,$(BUILDROOT),$(JULIA_EXECUTABLE)) | tr / '\\')" '%*' > $(BUILDROOT)/julia.bat
+	@echo '@"%~dp0\'"$$(echo $(call rel_path,$(BUILDROOT),$(JULIA_EXECUTABLE)) | tr / '\\')"\" '%*' > $(BUILDROOT)/julia.bat
 	chmod a+x $(BUILDROOT)/julia.bat
 else
 ifndef JULIA_VAGRANT_BUILD