fix: fake mailer assert methods

[RomainLanz]

Could you please explain your changes?

[memsbdm]

@RomainLanz previous methods used in docs (assertHasTo, assertHasFrom, ..) doesn't exist anymore. It should be / was replaced by assertTo, assertFrom, ...

Also these methods are not returning this anymore so we cannot chain them so I removed that part from the first example.

[RomainLanz]

Cool! I wonder if it wouldn't be better to add back the "chainability" of those assertions.

Let's see what @Julien-R44 or @thetutlage think.

[thetutlage]

The PR for docs matches the implementation. We can discuss about chaining of methods separately 🙂

[thetutlage]

Thanks @memsbdm