Actually fix build

ImGuiHoveredFlags_Default isn't a valid identifier. It seems it perhaps was at some point, but the
flag that's in the api is ImGuiHoveredFlags_None. I see the former mentioned in ocornut#1382,
and its description is the same as what is now given to None.

imgui_user.inl

@@ -76,7 +76,7 @@ namespace ImGui
 		if (!ItemAdd(bb, 0))
 			return 0;
 
-		const bool hovered = IsItemHovered(ImGuiHoveredFlags_Default);
+		const bool hovered = IsItemHovered(ImGuiHoveredFlags_None);
 
 		int max = 0;
 		while (max < maxpoints && points[max].x >= 0) max++;
@@ -248,7 +248,7 @@ namespace ImGui
 			return 0;
 		}
 
-		const bool hovered = IsItemHovered(ImGuiHoveredFlags_Default);
+		const bool hovered = IsItemHovered(ImGuiHoveredFlags_None);
 
 		int max = 0;
 		while (max < maxpoints && points[max].x >= 0) {