[uikit] NSLayoutContraint fixes (#435)

- Fix missing [Internal] attribute.
- Fix styling.

src/UIKit/NSLayoutConstraint.cs

@@ -25,13 +25,13 @@ namespace XamCore.UIKit {
 		[iOS (10, 0)]
 		public NSLayoutAnchor<AnchorType> FirstAnchor<AnchorType> () where AnchorType : NSObject
 		{
-			return  Runtime.GetNSObject<NSLayoutAnchor<AnchorType>> (_FirstAnchor ());
+			return Runtime.GetNSObject<NSLayoutAnchor<AnchorType>> (_FirstAnchor ());
 		}
 
 		[iOS (10, 0)]
 		public NSLayoutAnchor<AnchorType> SecondAnchor<AnchorType> () where AnchorType : NSObject
 		{
-			return  Runtime.GetNSObject<NSLayoutAnchor<AnchorType>> (_SecondAnchor ());
+			return Runtime.GetNSObject<NSLayoutAnchor<AnchorType>> (_SecondAnchor ());
 		}
 	}
 }

src/uikit.cs

@@ -341,6 +341,7 @@ namespace XamCore.UIKit {
 	
 		[iOS (10, 0)]
 		[NullAllowed, Export ("secondAnchor", ArgumentSemantic.Copy)]
+		[Internal]
 		IntPtr _SecondAnchor<AnchorType> ();
 #endif
 	}