Update dependencies from https://github.com/dotnet/iot build 20190415.6 (#365)

- Iot.Device.Bindings - 0.1.0-prerelease.19215.6
- System.Device.Gpio - 0.1.0-prerelease.19215.6

eng/Version.Details.xml

 <?xml version="1.0" encoding="utf-8"?>
 <Dependencies>
   <ProductDependencies>
-    <Dependency Name="System.Device.Gpio" Version="0.1.0-prerelease.19215.5">
+    <Dependency Name="System.Device.Gpio" Version="0.1.0-prerelease.19215.6">
       <Uri>https://github.com/dotnet/iot</Uri>
-      <Sha>909d6dd81bfdf35a2ab02f48ac54c5f30821ea8b</Sha>
+      <Sha>78a38a77f276c5c2e3486e1a0e0a1ecfbab3f860</Sha>
     </Dependency>
-    <Dependency Name="Iot.Device.Bindings" Version="0.1.0-prerelease.19215.5">
+    <Dependency Name="Iot.Device.Bindings" Version="0.1.0-prerelease.19215.6">
       <Uri>https://github.com/dotnet/iot</Uri>
-      <Sha>909d6dd81bfdf35a2ab02f48ac54c5f30821ea8b</Sha>
+      <Sha>78a38a77f276c5c2e3486e1a0e0a1ecfbab3f860</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.19215.5</SystemDeviceGpioPackageVersion>
-    <IotDeviceBindingsPackageVersion>0.1.0-prerelease.19215.5</IotDeviceBindingsPackageVersion>
+    <SystemDeviceGpioPackageVersion>0.1.0-prerelease.19215.6</SystemDeviceGpioPackageVersion>
+    <IotDeviceBindingsPackageVersion>0.1.0-prerelease.19215.6</IotDeviceBindingsPackageVersion>
   </PropertyGroup>
 </Project>