Frontend.XF.UWP: upgrade toolkit, to avoid mysterious errors

When trying the option "(right click on project->)Publish->Create App
Packages..." I was getting the error:

ILT0005: 'C:\Users\knoct\.nuget\packages\microsoft.net.native.compiler\2.0.2\tools\x64\ilc\ilc.exe --gatekeeper @"C:\Users\knoct\Source\Repos\geewalletFRONTEND\src\GWallet.Frontend.XF.UWP\obj\x64\Release\ilc\intermediate\gkargs.rsp"' returned exit code 1	GWallet.Frontend.XF.UWP

Which seemed to be a limiation of UWP wrt F#, but after bringing it up
in github[1] I was recommended to follow the recommendation of hacking
my local environment[2]. I did this in the recommended path:

C:\Program Files (x86)\Microsoft SDKs\UWPNuGetPackages\runtime.win10-x64.microsoft.net.native.compiler\2.2.7-rel-27913-00\tools\x64\ilc\tools\GatekeeperConfig.xml

But it didn't have any effect. So I did it in this path instead, which
seems more appropriate by reading the initial compilation error I had:

C:\Users\<MyUserName>\.nuget\packages\microsoft.net.native.compiler\2.0.2\tools\x64\ilc\tools\GatekeeperConfig.xml

But the result of doing this was this strange error:

Internal compiler error: Object reference not set to an instance of an object.

So I decided to upgrade the nuget packages of the project related to the
UWP SDK (from 6.0.4 to 6.2.9 as this diff shows), and it seems to have
helped here because I don't get this error anymore (but others which I'll
fix in subsequent commits).

[1] dotnet/corert#6055 (comment)
[2] dotnet/corert#5780 (comment)

src/GWallet.Frontend.XF.UWP/GWallet.Frontend.XF.UWP.csproj

@@ -18,6 +18,14 @@
     <ProjectTypeGuids>{A5A43C5B-DE2A-4C0C-9213-0A381AF9435A};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
     <WindowsXamlEnableOverview>true</WindowsXamlEnableOverview>
     <PackageCertificateKeyFile>GWallet.Frontend.XF.UWP_TemporaryKey.pfx</PackageCertificateKeyFile>
+    <GenerateAppInstallerFile>False</GenerateAppInstallerFile>
+    <AppxPackageSigningEnabled>False</AppxPackageSigningEnabled>
+    <AppxPackageSigningTimestampDigestAlgorithm>SHA256</AppxPackageSigningTimestampDigestAlgorithm>
+    <AppxAutoIncrementPackageRevision>True</AppxAutoIncrementPackageRevision>
+    <GenerateTestArtifacts>True</GenerateTestArtifacts>
+    <AppxBundle>Always</AppxBundle>
+    <AppxBundlePlatforms>x64</AppxBundlePlatforms>
+    <HoursBetweenUpdateChecks>0</HoursBetweenUpdateChecks>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'Debug|x86'">
     <DebugSymbols>true</DebugSymbols>
@@ -123,7 +131,7 @@
   </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform">
-      <Version>6.0.4</Version>
+      <Version>6.2.9</Version>
     </PackageReference>
     <PackageReference Include="Xamarin.Forms">
       <Version>4.5.0.266-pre3</Version>