Merge pull request #552 from ServiceStack/postgres-core-nuget-update

Update to 3.1.8 as fails to find DLL at runtime.

Author: mythz

NuGet.Core/ServiceStack.OrmLite.PostgreSQL.Core/ServiceStack.OrmLite.PostgreSQL.Core.nuspec

@@ -19,7 +19,7 @@
     <copyright>Copyright 2016 Service Stack</copyright>
     <dependencies>
       <group targetFramework=".NETStandard1.3">
-        <dependency id="Npgsql" version="[3.1.7, )" />
+        <dependency id="Npgsql" version="[3.1.8, )" />
         <dependency id="ServiceStack.Interfaces.Core" version="[1.0.0, )" />
         <dependency id="ServiceStack.Text.Core" version="[1.0.0, )" />
         <dependency id="ServiceStack.Common.Core" version="[1.0.0, )" />