Downgrade to stable packages

build/common.props

@@ -1,4 +1,5 @@
 <Project>
+  <Import Project="dependencies.props" />
   <Import Project="..\version.props" />
 
   <PropertyGroup>

build/dependencies.props

@@ -0,0 +1,6 @@
+<Project>
+  <PropertyGroup>
+    <NetStandardImplicitPackageVersion>1.6.1</NetStandardImplicitPackageVersion>
+    <CoreFxVersion>4.3.0</CoreFxVersion>
+  </PropertyGroup>
+</Project>