Update dependencies from https://github.com/dotnet/winforms build 20190905.20 (#1792)

- Microsoft.Private.Winforms - 4.8.0-rc1.19455.20

Author: dotnet-maestro[bot]

eng/Version.Details.xml

@@ -1,9 +1,9 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Dependencies>
   <ProductDependencies>
-    <Dependency Name="Microsoft.Private.Winforms" Version="4.8.0-rc1.19455.19">
+    <Dependency Name="Microsoft.Private.Winforms" Version="4.8.0-rc1.19455.20">
       <Uri>https://github.com/dotnet/winforms</Uri>
-      <Sha>3a863ab47f3278df39805654db9f9b0516eb8dba</Sha>
+      <Sha>9104c48ca015b5a4c8e029c330af6d68bc11b0b8</Sha>
     </Dependency>
   </ProductDependencies>
   <ToolsetDependencies>

eng/Versions.props

@@ -8,7 +8,7 @@
   </PropertyGroup>
   <!-- NuGet Package Versions -->
   <PropertyGroup>
-    <MicrosoftPrivateWinformsVersion>4.8.0-rc1.19455.19</MicrosoftPrivateWinformsVersion>
+    <MicrosoftPrivateWinformsVersion>4.8.0-rc1.19455.20</MicrosoftPrivateWinformsVersion>
   </PropertyGroup>
   <!-- Packages that come from https://github.com/dotnet/coreclr -->
   <PropertyGroup>