Small errata in page 59

[Santiago Sanchez]

In page 59 on section 3.3 there is a small errata which says the following.

Although there are various tools to transpile JSX, the most frequently used tool—
and the one recommended by the React team on the official React website, as of
August 2016—is Babel (formerly, 5to6).

Is 6to5 instead of 5to6.