Updated `doc/opcode.md` to match `include/mruby/ops.h` [ci skip]

Comment out `warn` used in the `Array#fetch` method

I get an error because the current mruby does not have a `Kernel#warn` method.
But the warning itself is useful and I'll just comment it out in case it's implemented in the future.

The issue is reported by @shuujii.

Fix type tag that set to `NilClass` and `FalseClass`

Skip --depth=1 when it's locked

Add `-s` option to `mrbc` for make variable static

Bump actions/upload-artifact from v1 to v2.2.2

Bump actions/cache from v2 to v2.1.4

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from v1 to v2.2.2.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v1...e448a9b857ee2131e752b06002bf0e093c65e571)
Signed-off-by: dependabot[bot] <support@github.com>

Bumps [actions/cache](https://github.com/actions/cache) from v2 to v2.1.4.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](https://github.com/actions/cache/compare/v2...26968a09c0ea4f3e233fdddbafd1166051a095f6)
Signed-off-by: dependabot[bot] <support@github.com>

feat: add Dependabot config file

For better coverage.

Refine checking for trailing whitespace [skip travis][skip appveyor]

Remove trailing tab in `build_config/dreamcast_shelf.rb` [ci skip]

Introduce EditorConfig [skip ci]

Place optable in ROM

* Include tabs in checking.
* Use `git grep` to avoid including `.git` directory.
* Avoid running `grep` multiple times.

refactor: add the spell checker Action to the Lint Action file

Order jobs in workflow.

chore: fix missing HTTPS on links

chore: fix spelling

Set for GitHub Actions to check for update everyday.

When you add or update the dependabot.yml file, this triggers an immediate check for version updates. Any options that also affect security updates are used the next time a security alert triggers a pull request for a security update.

https://docs.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates

Normally a single spell checker can't find all the mistakes or check all types of code.

These mistakes were found by another spell checker inside my editor with a more manual sift / find.

feat(CI): check for trailing whitespace