Typos in "learn-golang.org/en/Functions"

[gcsandesh]

There are some typos in this page: https://www.learn-golang.org/en/Functions

Here are the screenshots:

Also there are missing punctuation marks in some places.

I would like to contribute by solving this issue if you assign it to me.

[gcsandesh]

I read the contributing tutorial here and have created a PR that fixes this issue.