requireShorthandArrowFunctions should not fire for functions that do not return

[fluky]

Probably just needs a new option for requireShorthandArrowFunctions.

Consider the case:

() => { return something; }

This should trigger. But

() => { something (); }

Should not trigger.

The reason is that the latter returns undefined instead of the result of something which could have a different effect in the code calling the function.

[markelog]

At this point only major and CST related bugs will be fixed.