Release 4.0.0-rc.0

• Housekeeping (13e9336)
• Switch to shell.exec by default (instead of dedicated shelljs methods) (b019d98)
• Mock stdout with mock-stdio (64a35ca)
• fix(package): update supports-color to version 4.5.0 (106a484)
• fix(package): update chalk to version 2.2.0 (af323f9)

Breaking change

In short, this does not affect you if you didn't use the ! prefix in command hooks such as buildCommand.

Before, the buildCommand and other command hooks could have a ! prefix to enforce it not to use ShellJS internal commands. This was especially required for combined commands such as "!npm test && npm run build". However, from release-it v4, the default is to always resort to shell.exec. To enforce usage of internal ShellJS commands, the command should be prefixed with ! (e.g. "!mkdir -p build").