Fix a typo in ch17

ch17_fold.md

@@ -363,6 +363,6 @@ By default, Vim saves the fold information when running `mkview` inside `~/.vim/
 
 ## Learn Fold the Smart Way
 
-When I first started Vim, I neglected ot learn fold because I didn't think it was useful. However, the longer I code, the more useful I find folding is. Strategically placed folds can give you a better overview of the text structure, like a book's table of content.
+When I first started Vim, I neglected to learn fold because I didn't think it was useful. However, the longer I code, the more useful I find folding is. Strategically placed folds can give you a better overview of the text structure, like a book's table of content.
 
 When you learn fold, start with the manual fold because that can be used on-the-go. Then gradually learn different tricks to do indent and marker folds. Finally, learn how to do syntax and expression folds. You can even use the latter two to write your own Vim plugins.