Update dependencies from https://github.com/dotnet/iot build 20190531.2 (#468)

- Iot.Device.Bindings - 0.1.0-prerelease.19281.2
- System.Device.Gpio - 0.1.0-prerelease.19281.2

eng/Version.Details.xml

 <?xml version="1.0" encoding="utf-8"?>
 <Dependencies>
   <ProductDependencies>
-    <Dependency Name="System.Device.Gpio" Version="0.1.0-prerelease.19280.2">
+    <Dependency Name="System.Device.Gpio" Version="0.1.0-prerelease.19281.2">
       <Uri>https://github.com/dotnet/iot</Uri>
-      <Sha>1e66f53f1398440107e8d2ca736c3e330a19cdc2</Sha>
+      <Sha>ad333e9a890e044948f02d287214a5168fed24e4</Sha>
     </Dependency>
-    <Dependency Name="Iot.Device.Bindings" Version="0.1.0-prerelease.19280.2">
+    <Dependency Name="Iot.Device.Bindings" Version="0.1.0-prerelease.19281.2">
       <Uri>https://github.com/dotnet/iot</Uri>
-      <Sha>1e66f53f1398440107e8d2ca736c3e330a19cdc2</Sha>
+      <Sha>ad333e9a890e044948f02d287214a5168fed24e4</Sha>
     </Dependency>
   </ProductDependencies>
   <ToolsetDependencies>

eng/Versions.props

@@ -2,7 +2,7 @@
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
     <PreReleaseVersionLabel>prerelease</PreReleaseVersionLabel>
-    <SystemDeviceGpioPackageVersion>0.1.0-prerelease.19280.2</SystemDeviceGpioPackageVersion>
-    <IotDeviceBindingsPackageVersion>0.1.0-prerelease.19280.2</IotDeviceBindingsPackageVersion>
+    <SystemDeviceGpioPackageVersion>0.1.0-prerelease.19281.2</SystemDeviceGpioPackageVersion>
+    <IotDeviceBindingsPackageVersion>0.1.0-prerelease.19281.2</IotDeviceBindingsPackageVersion>
   </PropertyGroup>
 </Project>