Installing should package

[nunorafaelrocha]

Since should package is registered as a devDependency and peerDependency, anyone that follows the instructions and isn't using should runs into an UNMET PEER DEPENDENCY warning followed by a Cannot find module 'should' error when running jscs.

The package is used in the requireShouldAssertionExecution rule, so I think we have two options:

1. Move should from devDependencies to dependencies.
2. Add should to the installation instructions on README.md.

[ruimarinho]

This is definitely a dependency, not a dev or peer one. I probably think it'd be easier to simply list the methods where they are necessary.

[ruimarinho]

@ruiquelhas can you take of this? https://github.com/seegno/jscs-config-seegno/blame/master/src/rules/require-should-assertion-execution.js#L8 we can either cache this or mark this a dependency instead.

[ruiquelhas]

We have the same issue for jscs, although that one is part of the installation instructions. They were peerDependencies before, to avoid this kind of issues (or at least to provide proper installation warnings).

I'm not sure if it's a good idea to move them to the dependencies, so I would suggest to just add should to the installation instructions.

[ruimarinho]

I have a better solution for this I think - invoke the require call inside a try catch and only add this rule if the should package is installed. Since most dev envs will already have it, those who forget to install it or are simply not interested in loading it, will not suffer from it.

[fixe]

Not solved by #23. We still need to implement @ruimarinho suggestion.