Fixes some misspelling in readme file

[hfvmarques]

Description

What?

I found a few words misspelled in the readme file.

Why?

I really want to contribute more with open source and this is how I think I can contribute for now until I start using the gem for myself in my applications.

How

Either correcting the words misspelled or changing it for another word which I found is better for the context

[igorkasyanchuk]

thanks!