Update dependencies from https://github.com/dotnet/standard build 20190408.1 (#5725)

- NETStandard.Library - 2.1.0-prerelease.19208.1

eng/Version.Details.xml

@@ -13,9 +13,9 @@
       <Uri>https://github.com/dotnet/corefx</Uri>
       <Sha>8321c729934c0f8be754953439b88e6e1c120c24</Sha>
     </Dependency>
-    <Dependency Name="NETStandard.Library" Version="2.1.0-prerelease.19207.1">
+    <Dependency Name="NETStandard.Library" Version="2.1.0-prerelease.19208.1">
       <Uri>https://github.com/dotnet/standard</Uri>
-      <Sha>040f41f20972988aa34195e778b4170004ead695</Sha>
+      <Sha>16f3d7537987f094cac266152a17e8ed6c4c440f</Sha>
     </Dependency>
     <Dependency Name="Microsoft.NETCore.Runtime.CoreCLR" Version="3.0.0-preview4-27604-73">
       <Uri>https://github.com/dotnet/coreclr</Uri>

eng/Versions.props

@@ -12,7 +12,7 @@
     <MicrosoftNETCorePlatformsPackageVersion>3.0.0-preview5.19208.1</MicrosoftNETCorePlatformsPackageVersion>
     <MicrosoftNETCoreTargetsPackageVersion>2.0.0</MicrosoftNETCoreTargetsPackageVersion>
     <!-- standard -->
-    <NETStandardLibraryPackageVersion>2.1.0-prerelease.19207.1</NETStandardLibraryPackageVersion>
+    <NETStandardLibraryPackageVersion>2.1.0-prerelease.19208.1</NETStandardLibraryPackageVersion>
     <!-- coreclr -->
     <MicrosoftNETCoreRuntimeCoreCLRPackageVersion>3.0.0-preview4-27604-73</MicrosoftNETCoreRuntimeCoreCLRPackageVersion>
     <!-- dotnet-trusted -->