User guide references deprecated `check` function

[ryantate]

The namespace docs state clearly that buddy.hashers/check "Should be considered as DEPRECATED" in preference of buddy.hashers/verify.

In the User Guide, the examples correctly use verify, but other parts of the text contain references to check, which in both cases are vestigial and incorrect.

Instance 1:

Hashers module consists in two public functions: derive and check and both them are located on buddy.hashers namespace.

Instance 2:

Some times you don’t want to use all the supported algorithms and you only want to use a own set of algorithms in the password check process. That can be done passing additional parameter to the check function:

This is followed by an example using verify instead of check.

I'd be happy to contribute a pull request if that is welcome.