Made issues.go check if arg is a file

cmd/issues.go

@@ -32,6 +32,9 @@ func main() {
 				fmt.Printf("%s is a directory...\n", arg[0])
 				os.Exit(1)
 			}
+		} else {
+			fmt.Printf("%s is an existing file...\n", arg[0])
+			os.Exit(1)
 		}
 	}