Add back .NET Core 3 target until .NET Core 3 runtime has the latest netstandard dll in it.

Ix.NET/Source/System.Interactive.Async.Providers/System.Interactive.Async.Providers.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <Description>Interactive Extensions Async Providers Library used to build query providers and express queries over async enumerable sequences.</Description>
     <AssemblyTitle>Interactive Extensions - Async Providers Library</AssemblyTitle>
-    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1;netcoreapp3.0</TargetFrameworks>
     <PackageTags>Ix;Interactive;Extensions;Enumerable;Asynchronous</PackageTags>
   </PropertyGroup>
 

Ix.NET/Source/System.Interactive.Async/System.Interactive.Async.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <Description>Interactive Extensions Async Library used to express queries over asynchronous enumerable sequences.</Description>
     <AssemblyTitle>Interactive Extensions - Async Library</AssemblyTitle>
-    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1;netcoreapp3.0</TargetFrameworks>
     <PackageTags>Ix;Interactive;Extensions;Enumerable;Asynchronous</PackageTags>
   </PropertyGroup>
 

Ix.NET/Source/System.Linq.Async.Queryable/System.Linq.Async.Queryable.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1;netcoreapp3.0</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>

Ix.NET/Source/System.Linq.Async/System.Linq.Async.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net45;net46;netstandard2.0;netstandard2.1;netcoreapp3.0</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>

Ix.NET/Source/refs/System.Linq.Async.Ref/System.Linq.Async.Ref.csproj

@@ -4,7 +4,7 @@
     <Description>LINQ Standard Query Operators used to express queries over asynchronous enumerable sequences.</Description>
     <AssemblyTitle>System.Linq.Async</AssemblyTitle>
     <Authors>Microsoft</Authors>
-    <TargetFrameworks>net45;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>net45;netstandard2.0;netstandard2.1;netcoreapp3.0</TargetFrameworks>
     <PackageTags>Enumerable;Asynchronous;LINQ</PackageTags>
   </PropertyGroup>