Mark `-[init]` w RCT_NOT_IMPLEMENTED

Summary: ARTBrush.m doesn't defined init but Clang wants it.

Fix #2590
Closes https://github.com/facebook/react-native/pull/2592

Reviewed By: svcscm

Differential Revision: D2656454

Pulled By: nicklockwood

fb-gh-sync-id: c386adfadc30c5a0b642b60d3b7e1991481f1fb9

Libraries/ART/Brushes/ARTBrush.m

@@ -9,6 +9,8 @@
 
 #import "ARTBrush.h"
 
+#import "RCTDefines.h"
+
 @implementation ARTBrush
 
 - (instancetype)initWithArray:(NSArray *)data
@@ -16,6 +18,8 @@
   return [super init];
 }
 
+RCT_NOT_IMPLEMENTED(- (instancetype)init)
+
 - (BOOL)applyFillColor:(CGContextRef)context
 {
   return NO;