Fixed default placeholder text color for multiline <TextInput>

Reviewed By: javache

Differential Revision: D5018823

fbshipit-source-id: 6ad4a1e8d03b6429a436e0cfdd9a127cd5dc1c2b

Libraries/Text/RCTUITextView.m

@@ -39,6 +39,7 @@ static UIColor *defaultPlaceholderTextColor()
     _placeholderView = [[UILabel alloc] initWithFrame:self.bounds];
     _placeholderView.isAccessibilityElement = NO;
     _placeholderView.numberOfLines = 0;
+    _placeholderView.textColor = defaultPlaceholderTextColor();
     [self addSubview:_placeholderView];
   }