fixed Fable compile problems

Author: krauthaufen

src/FSharp.Data.Adaptive/AdaptiveIndexList/AdaptiveIndexList.fs

@@ -2,6 +2,7 @@ namespace FSharp.Data.Adaptive
 
 open System
 open FSharp.Data.Traceable
+open FSharp.Data.Adaptive
 
 /// An adaptive reader for alist that allows to pull operations and exposes its current state.
 type IIndexListReader<'T> = 

src/FSharp.Data.Adaptive/AdaptiveIndexList/AdaptiveIndexList.fsi

@@ -2,6 +2,7 @@
 
 open System
 open FSharp.Data.Traceable
+open FSharp.Data.Adaptive
 
 /// An adaptive reader for alist that allows to pull operations and exposes its current state.
 type IIndexListReader<'T> = 

src/FSharp.Data.Adaptive/FSharp.Data.Adaptive.fsproj

@@ -2,7 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <OutputType>Library</OutputType>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFrameworks>netstandard2.0;netcoreapp3.1</TargetFrameworks>
     <DisableImplicitFSharpCoreReference>true</DisableImplicitFSharpCoreReference>
   </PropertyGroup>
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">