Documentation: update pitfalls section

[travis-leith]

It is not clear to me how this advice is out of date.

The documentation states "Applies only to Fable 2.x". This either means that the problems caused by these pitfalls are

• solved automagically by later versions of Fable
• still relevant but should be demonstrated with some other syntax that is available in later versions of Fable

Please remove this ambiguity by one of the following

• Remove this page
• Update the page to state that these problems do not exist at all in later versions of Fable
• Update the page to use the most recent syntax and remove the caveat about Fable 2.x.
• Something else to make clear how this advice relates to Fable version.

I am happy to raise a PR to this effect if someone can confirm to me (in this issue) the correct action to take.