Update .travis.yml

The patch is created by @take_cheese in #3872

The patch is created by @take_cheese in #3872

Some test may be OK but we skip everything as a starting point.

Skip "File.readlink fails" test on MSVC

Use same format between Fail and Skip

When MSVC, "File.readlink fails with non-symlink" test was failed even if raising NotImplementedError

We can see gem name in skip message by this fix

Fixed compile error of `mruby-io` gem on MinGW.

Fix memory leak found by leak sanitizer.

- `mode_t` by `int`
- `umask` by `_umask`
- `rmdir` by `_rmdir`
- `mkstemp` and `mkdtemp` by using `_mktemp`

git-subtree-dir: mrbgems/mruby-pack
git-subtree-mainline: 842e6945
git-subtree-split: 383a9c79

Also `bool` is a reserved word in C++.

git-subtree-dir: mrbgems/mruby-socket
git-subtree-mainline: d75266dd
git-subtree-split: ab541850

git-subtree-dir: mrbgems/mruby-io
git-subtree-mainline: 10ed730e
git-subtree-split: 3c8e1f94

The code was introduced to address #3175 but it's no longer needed.

Otherwise `super` may call a wrong method.

Mentioned in https://qiita.com/bamchoh/items/eabebbbb330cb0e0470a