jshn: main: fix leak of memory pointed to by 'vars'

Fixes following leak of memory:

 6,016 bytes in 1 blocks are possibly lost in loss record 1 of 1
    at 0x4C31B25: calloc
    by 0x1098F8: main (jshn.c:353)

Signed-off-by: Petr Štetiar <ynezz@true.cz>

jshn.c

@@ -443,12 +443,15 @@ int main(int argc, char **argv)
 			indent = true;
 			break;
 		default:
+			free(vars);
 			return usage(argv[0]);
 		}
 	}
 
+	free(vars);
 	return usage(argv[0]);
 
 exit:
+	free(vars);
 	return ret;
 }