Maintain project

- Update .NET SDK on CI
- Update Ruby on CI
- Embed icon to the NuGet package

Author: zvirja

.travis.yml

@@ -1,8 +1,8 @@
 language: csharp
 dist: xenial
-dotnet: 2.1.502
+dotnet: 5.0.100
 mono: none
-env: CONFIGURATION=Release FRAMEWORK=netcoreapp2.1
+env: CONFIGURATION=Release FRAMEWORK=net5.0
 
 before_script:
   - dotnet --info

appveyor.yml

@@ -1,11 +1,11 @@
-os: Visual Studio 2017
+os: Visual Studio 2019
 build: off
 
 environment:
   CONFIGURATION: Release
 
 install:
-  - set PATH=C:\Ruby22\bin;%PATH%
+  - set PATH=C:\Ruby25\bin;%PATH%
   - bundle install      
 
 before_test:

src/NSubstitute/NSubstitute.csproj

@@ -7,10 +7,13 @@
     <AssemblyName>NSubstitute</AssemblyName>
     <PackageId>NSubstitute</PackageId>
     <PackageTags>mocking;mocks;testing;unit-testing;TDD;AAA</PackageTags>
-    <PackageIconUrl>https://nsubstitute.github.io/images/nsubstitute-100x100.png</PackageIconUrl>
+    <PackageIcon>icon.png</PackageIcon>
     <PackageProjectUrl>https://nsubstitute.github.io/</PackageProjectUrl>
     <PackageLicenseExpression>BSD-3-Clause</PackageLicenseExpression>
   </PropertyGroup>
+  <ItemGroup>
+    <None Include="..\..\docs\images\nsubstitute-100x100.png" Pack="true" PackagePath="icon.png" Visible="false" />
+  </ItemGroup>
 
   <PropertyGroup>
     <TargetFrameworks>netstandard1.3;netstandard2.0;net45;net46;net5.0</TargetFrameworks>