Update WavFile.csproj

[skip ci]

src/WavFile/WavFile.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard1.1;net45</TargetFrameworks>
+    <TargetFrameworks>netstandard1.3;net45</TargetFrameworks>
     <OutputType>Library</OutputType>
     <EnableDefaultCompileItems>False</EnableDefaultCompileItems>
     <GenerateAssemblyInfo>False</GenerateAssemblyInfo>
@@ -32,6 +32,6 @@
     <Compile Include="**\*.cs" Exclude="obj\**" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="System.IO" Version="4.3.0" />
+    <PackageReference Include="System.IO.FileSystem" Version="4.3.0" />
   </ItemGroup>
 </Project>