Typo fix

Author: tomayac

index.bs

@@ -292,7 +292,7 @@ Use Cases and Requirements {#usecases-requirements}
 
 - A Web application provides input for a smart home system to control lighting.
 - A Web aplication checks whether light level at work space is sufficient.
-- A Web application calculates settings for a camera with manual controls (apperture, shutter speed, ISO).
+- A Web application calculates settings for a camera with manual controls (aperture, shutter speed, ISO).
 - A Web application monitors light level changes produced by hovering hand user gesture and
   interprets them to control a game character.