Makefile: Avoid executing the hint (#3564)

Backticks execute the command even when they are in quotes.

Makefile

@@ -67,7 +67,7 @@ clean-hint:
 	@echo -e "\n\n\n>>> PSA: if you get errors that are hard to explain,"
 	@echo -e ">>> try 'git submodule update --init --recursive' and 'make full-clean' and run your command again."
 	@echo -e ">>> see https://github.com/wireapp/wire-server/blob/develop/docs/developer/building.md#linker-errors-while-compiling"
-	@echo -e ">>> to never have to remember submodules again, try `git config --global submodule.recurse true`"
+	@echo -e ">>> to never have to remember submodules again, try 'git config --global submodule.recurse true'"
 	@echo -e "\n\n\n"
 
 .PHONY: cabal.project.local