Merge pull request #62 from VasileDurlesteanu/master

update README.md

Author: sudheerj

README.md

@@ -913,7 +913,7 @@ You can download the PDF and Epub version of this repository from the latest run
  **[⬆ Back to Top](#table-of-contents)**
 
 31. ### What is a custom pipe?
- Apart from built-inn pipes, you can write your own custom pipe with the below key characteristics,
+ Apart from built-in pipes, you can write your own custom pipe with the below key characteristics:
  1. A pipe is a class decorated with pipe metadata **@Pipe** decorator, which you import from the core Angular library
  For example,
  ```javascript