isIOS and isAndroid utils are now constants instead of functions

lib/utils/index.js

@@ -87,21 +87,9 @@ export function isString(value): Boolean {
   return typeof value === 'string';
 }
 
-/**
- * Returns true if on ios
- * @returns {boolean}
- */
-export function isIOS() {
-  return Platform.OS === 'ios';
-}
-
-/**
- * Returns true if on android
- * @returns {boolean}
- */
-export function isAndroid() {
-  return Platform.OS === 'android';
-}
+// platform checks
+export const isIOS = Platform.OS === 'ios';
+export const isAndroid = Platform.OS === 'android';
 
 
 /**