Update Directory.Build.props

Author: SimonCropp

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
   <PropertyGroup>
     <NoWarn>CS1591;CS0649;xUnit1026;xUnit1013;msb3277;CS0436</NoWarn>
-    <Version>17.9.0-beta.1</Version>
+    <Version>17.9.0</Version>
     <ImplicitUsings>enable</ImplicitUsings>
     <LangVersion>preview</LangVersion>
     <SuppressTfmSupportBuildWarnings>true</SuppressTfmSupportBuildWarnings>