Excessive error messages when using `--if` argument.

Not sure if this is expected behavior or not.

if you run `yarn wsrun --if ...` and the condition script failed, error messages like these are in the output:
```
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
```
but these are not useful information, it is expected for the command to fail when the if condition does not met.

In the code, `wsrun` always set `silent` option to `true` if the command is used for the `--if` argument, but the code is not checking `silent` flag before output to console, I have to add `if (!this.opts.silent)` on line https://github.com/hfour/wsrun/blob/0a75328dfb178740d22cdcbf19462d58edad90e6/src/cmd-process.ts#L154 and https://github.com/hfour/wsrun/blob/0a75328dfb178740d22cdcbf19462d58edad90e6/src/cmd-process.ts#L159 to mute all the output for command evaluation results, so that I can mute all output for commands used in `--if` arguments.

In this case, should `wsrun` write anything to console if `silent` is set to true? If yes, can we add a command line option to mute all output for the commands used as if conditions?