chore(docs): Correct the spelling of Bootstrap 4 (#3184)

Author: demus

README.md

@@ -373,7 +373,7 @@ Some javascript libraries need to be added to the global scope, and loaded as if
 they were in a script tag. We can do this using the `apps[0].scripts` and
 `apps[0].styles` properties of `angular-cli.json`.
 
-As an example, to use [Boostrap 4](http://v4-alpha.getbootstrap.com/) this is
+As an example, to use [Bootstrap 4](http://v4-alpha.getbootstrap.com/) this is
 what you need to do:
 
 First install Bootstrap from `npm`: