add: fix test with ` around DVC command

Author: jorgeorpinel

tests/func/test_add.py

@@ -92,7 +92,7 @@ def test_warn_about_large_directories(self):
             "You are adding a large directory 'large-dir' recursively,"
             " consider tracking it as a whole instead.\n"
             "{purple}HINT:{nc} Remove the generated DVC-file and then"
-            " run {cyan}dvc add large-dir{nc}".format(
+            " run `{cyan}dvc add large-dir{nc}`".format(
                 purple=colorama.Fore.MAGENTA,
                 cyan=colorama.Fore.CYAN,
                 nc=colorama.Style.RESET_ALL,