Let's use newer version

DOCX/DOCX.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>netcoreapp2.0</TargetFramework>
+        <TargetFramework>netcoreapp3.1</TargetFramework>
     </PropertyGroup>
 
     <ItemGroup>

DOCXTests/DOCXTests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
-        <TargetFramework>netcoreapp2.0</TargetFramework>
+        <TargetFramework>netcoreapp3.1</TargetFramework>
 
         <IsPackable>false</IsPackable>
     </PropertyGroup>