Use StandardError over Exception

[denys281]

Based on discussion: https://github.com/rubocop-hq/rubocop/pull/7325/files#r320964544

Rubocop issue: rubocop/rubocop#7299

[bquorning]

Perhaps this section should include a sentence about why one should not raise Exception.

[denys281]

Could you help with wording?

[pirj]

@denys281 Would "[Exception] will bypass test frameworks and error reporters" do?

[denys281]

@marcandre Could you take a look? Cop w merged some time ago.

[marcandre]

This PR still needs work...
It's true one should not raise an Exception, but it is not true one should raise a StandardException; it's more an abstract base class than anything else.
One should raise the appropriate exception (e.g. TypeError) or if nothing fits, a RuntimeError (which shouldn't be specified).
Maybe it would be best to modify the "don't rescue Exception" section, as they are related... Don't raise one because you should not rescue those...

[pirj]

Ping @denys281