minor text changes

This pull request corrects some typos and makes some minor changes to the text. I'm happy to revise these if requested.

1) Line 1 - Removed 'hopefully'. This tutorial step taught me successfully to use async.series, so the intro doesn't need to sound doubtful, and IMHO the sentence is a bit clearer without this word. 

2) Line 3 - Fixed minor typos and adjusted line breaks. Changed "wont pass it along" to "won't be passed along", as this seems to describe the behaviour better.

3) Line 26 - Fixed minor typo, added a comma, and adjusted line breaks. 

4) Line 48 - Added a comma, and adjusted line breaks.