Revert "Aim a little higher with targets."

This reverts commit b930a13461a65a3e3b26d33ce78958247ac9ae7a.

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

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <Description>Interactive Extensions Providers Library used to build query providers and express queries over enumerable sequences.</Description>
     <AssemblyTitle>Interactive Extensions - Providers Library</AssemblyTitle>
-    <TargetFrameworks>net461;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>net45;netstandard1.0;netstandard2.0</TargetFrameworks>
     <PackageTags>Ix;Interactive;Extensions;Enumerable</PackageTags>
   </PropertyGroup>
 
@@ -20,6 +20,10 @@
     <ReferenceAssemblyProjectReference Include="..\refs\System.Interactive.Providers.Ref\System.Interactive.Providers.Ref.csproj" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.0'">
+    <PackageReference Include="System.Linq.Queryable" Version="4.3.0" />
+  </ItemGroup>
+
   <ItemGroup>
     <None Update="System\Linq\QueryableEx.Generated.tt">
       <LastGenOutput>QueryableEx.Generated.cs</LastGenOutput>

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

@@ -4,7 +4,7 @@
     <Description>Interactive Extensions Main Library used to express queries over enumerable sequences.</Description>
     <AssemblyTitle>Interactive Extensions - Main Library</AssemblyTitle>
     <Authors>Microsoft</Authors>
-    <TargetFrameworks>net461;netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>net45;netstandard1.0;netstandard2.0</TargetFrameworks>
     <PackageTags>Ix;Interactive;Extensions;Enumerable</PackageTags>
   </PropertyGroup>