A recent commit in RN added start/end properties to RCTViewManager.
Because LinearGradient inherits from this class and has properties of
the same name, RN gets mixed up and tries to convert to a YGValue
instead of CGPoint, which results in the exception:
```
Error setting property 'start' of BVLinearGradient with tag #18: JSON
value '{
x = 0;
y = 0;
}' of type NSMutableDictionary cannot be converted to a YGValue.
```
Sam Mueller
rh389
Dmitry Gladkov