NONE: fix a bug of the memory checking

[kmyk]

time コマンドの呼び出したプログラムのリターンコードが非0だった場合にエラーになることに気付きました。次に示すような Command exited with ... という行が紛れ込んできて落ちます。これを修正します。

$ \time -f %M -- perl -e 'die "hoge"'
hoge at -e line 1.
Command exited with non-zero status 255
4840

$ oj t
[*] 3 cases found

[*] sample-1
/usr/bin/../lib/gcc/x86_64-linux-gnu/7.4.0/../../../../include/c++/7.4.0/debug/vector:417:
Error: attempt to subscript container with out-of-bounds index 7, but 
container only holds 7 elements.

Objects involved in the operation:
    sequence "this" @ 0x0x11adf88 {
      type = std::__debug::vector<int, std::allocator<int> >;
    }
Traceback (most recent call last):
  File "/home/user/.local/bin/oj", line 10, in <module>
    sys.exit(main())
  File "/home/user/.local/lib/python3.6/site-packages/onlinejudge/_implementation/main.py", line 284, in main
    run_program(namespace, parser=parser)
  File "/home/user/.local/lib/python3.6/site-packages/onlinejudge/_implementation/main.py", line 263, in run_program
    test(args)
  File "/home/user/.local/lib/python3.6/site-packages/onlinejudge/_implementation/command/test.py", line 213, in test
    history += [test_single_case(name, paths['in'], paths.get('out'), args=args)]
  File "/home/user/.local/lib/python3.6/site-packages/onlinejudge/_implementation/command/test.py", line 137, in test_single_case
    info, proc = utils.exec_command(args.command, stdin=inf, timeout=args.tle, gnu_time=args.gnu_time)
  File "/home/user/.local/lib/python3.6/site-packages/onlinejudge/_implementation/utils.py", line 166, in exec_command
    memory = int(fh1.read()) / 1000  # type: Optional[float]
ValueError: invalid literal for int() with base 10: 'Command terminated by signal 6\n3808\n'

@fukatani これは放置できないのでレビューを待たずにマージしてバージョンを上げます