Fix typo on 08_concurrency.md

it can have it's own internal multiplexing -> it can have its own internal multiplexing

12factor/08_concurrency.md

@@ -7,7 +7,7 @@ The app can be seen as a set of processes of different types
 * worker
 * cron
 
-Each process needs to be able to scale horizontally, it can have it's own internal multiplexing.
+Each process needs to be able to scale horizontally, it can have its own internal multiplexing.
 
 ## What does that mean for our application ?