Update dependencies from https://github.com/dotnet/standard build 20190729.2 (#39863)

- NETStandard.Library - 2.1.0-prerelease.19379.2

Author: dotnet-maestro[bot]

eng/Version.Details.xml

@@ -38,9 +38,9 @@
       <Uri>https://github.com/dotnet/arcade</Uri>
       <Sha>fb27fd4d8a2b67d4333e33d4b898c65171c9f3c1</Sha>
     </Dependency>
-    <Dependency Name="NETStandard.Library" Version="2.2.0-prerelease.19378.1">
+    <Dependency Name="NETStandard.Library" Version="2.1.0-prerelease.19379.2">
       <Uri>https://github.com/dotnet/standard</Uri>
-      <Sha>c6f3a338d8c9f3c37706c968d3f9ae54f280a971</Sha>
+      <Sha>56a4d43c963e533f5392c2c4f7b710f3ab98b5bd</Sha>
     </Dependency>
     <Dependency Name="Microsoft.DotNet.Helix.Sdk" Version="2.0.0-beta.19365.4">
       <Uri>https://github.com/dotnet/arcade</Uri>

eng/Versions.props

@@ -53,7 +53,7 @@
     <MicrosoftNETCorePlatformsPackageVersion>3.0.0-preview8.19365.14</MicrosoftNETCorePlatformsPackageVersion>
     <runtimenativeSystemIOPortsPackageVersion>4.6.0-preview8.19365.14</runtimenativeSystemIOPortsPackageVersion>
     <!-- Standard dependencies -->
-    <NETStandardLibraryPackageVersion>2.2.0-prerelease.19378.1</NETStandardLibraryPackageVersion>
+    <NETStandardLibraryPackageVersion>2.1.0-prerelease.19379.2</NETStandardLibraryPackageVersion>
     <!-- dotnet-optimization dependencies -->
     <optimizationwindows_ntx64IBCCoreFxPackageVersion>99.99.99-master-20190716.1</optimizationwindows_ntx64IBCCoreFxPackageVersion>
     <!-- sni -->