Minor textual update.

src/detect-engine-address.c

@@ -1102,7 +1102,7 @@ int DetectAddressMergeNot(DetectAddressHead *gh, DetectAddressHead *ghn)
     if (DetectAddressIsCompleteIPSpace(ghn) == 1) {
         SCLogError(SC_ERR_INVALID_SIGNATURE, "Complete IP space negated. "
                    "Rule address range is NIL. Probably have a !any or "
-                   "a address range that supplies a NULL address range");
+                   "an address range that supplies a NULL address range");
         goto error;
     }