Update why-webpack.md

[Stef733]

fix typo

[montogeek]

Not sure that is a typo.
cc @EugeneHlushko

[Stef733]

It's easy to confuse lets and let's :).

Let's is the shortened version of the words let us which is what is happening in the context of the sentence:
To understand why you should use webpack let's do a recap of how we...
You can check this works by changing the word to let us:
To understand why you should use webpack let us do a recap of how we...

Lets without the apostrophe can be thought of as a synonym of allow. E.g.
Webpack lets us bundle modules
is the same as
Webpack allows us to bundle modules.

If this is confusing, this link explains it better than I can :) - https://www.dictionary.com/e/lets/

[EugeneHlushko]

Yup this is good 👍

[EugeneHlushko]

Thanks!