Update uwp library version to 1.4 (#78)

Minor change in API for 1.4.
References updated.

Author: nickwinder

samples/Catalog/windows/Catalog/Catalog.csproj

@@ -224,7 +224,7 @@
     <SDKReference Include="Microsoft.VCLibs, Version=14.0">
       <Name>Visual C++ 2015 Runtime for Universal Windows Platform Apps</Name>
     </SDKReference>
-    <SDKReference Include="PSPDFKitSDK, Version=1.3.0">
+    <SDKReference Include="PSPDFKitSDK, Version=1.4.0">
       <Name>PSPDFKit for UWP</Name>
     </SDKReference>
   </ItemGroup>

windows/ReactNativePSPDFKit/ReactNativePSPDFKit/PDFViewPage.xaml.cs

@@ -17,8 +17,8 @@ public sealed partial class PDFViewPage : Page
     {
 
         Controller _controller;
-        const string _css = "ms-appx-web:///Assets/pspdfkit/windows.css";
-
+        private static Uri _css = new Uri("ms-appx-web:///Assets/pspdfkit/windows.css");
+    
         public PDFViewPage()
         {
             InitializeComponent();

windows/ReactNativePSPDFKit/ReactNativePSPDFKit/ReactNativePSPDFKit.csproj

@@ -122,7 +122,7 @@
     <SDKReference Include="Microsoft.VCLibs, Version=14.0">
       <Name>Visual C++ 2015 Runtime for Universal Windows Platform Apps</Name>
     </SDKReference>
-    <SDKReference Include="PSPDFKitSDK, Version=1.3.0">
+    <SDKReference Include="PSPDFKitSDK, Version=1.4.0">
       <Name>PSPDFKit for UWP</Name>
     </SDKReference>
   </ItemGroup>