fixed the bug on iOS that a fontFamily option does not effect when button state is disabled or highlighted (#3522)

lib/ios/RNNNavigationButtons.m

@@ -123,13 +123,17 @@
 	
 	NSNumber* fontSize = [self fontSize:dictionary[@"fontSize"] defaultFontSize:_defaultButtonStyle.fontSize];
 	NSString* fontFamily = [self fontFamily:dictionary[@"fontFamily"] defaultFontFamily:_defaultButtonStyle.fontFamily];
+	UIFont *font = nil;
 	if (fontFamily) {
-		[textAttributes setObject:[UIFont fontWithName:fontFamily size:[fontSize floatValue]] forKey:NSFontAttributeName];
-	} else{
-		[textAttributes setObject:[UIFont systemFontOfSize:[fontSize floatValue]] forKey:NSFontAttributeName];
+		font = [UIFont fontWithName:fontFamily size:[fontSize floatValue]];
+	} else {
+		font = [UIFont systemFontOfSize:[fontSize floatValue]];
 	}
+	[textAttributes setObject:font forKey:NSFontAttributeName];
+	[disabledTextAttributes setObject:font forKey:NSFontAttributeName];
 	
 	[barButtonItem setTitleTextAttributes:textAttributes forState:UIControlStateNormal];
+	[barButtonItem setTitleTextAttributes:textAttributes forState:UIControlStateHighlighted];
 	[barButtonItem setTitleTextAttributes:disabledTextAttributes forState:UIControlStateDisabled];
 	
 	NSString *testID = dictionary[@"testID"];