Update ASF to .NET Core 3.0 (#1427)

* Initial bump to .net core 3.0

* Update cc.sh

* Update appveyor.yml

* Update ArchiSteamFarm.csproj

* Update appveyor.yml

* Update .travis.yml

* Build corrections

* Cleanup

* Update .travis.yml

* Don't publish trimmed for now

* Update ArchiSteamFarm.csproj

ArchiSteamFarm.CustomPlugins.ExamplePlugin/ArchiSteamFarm.CustomPlugins.ExamplePlugin.csproj

@@ -18,11 +18,11 @@
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(OS)' == 'Windows_NT' OR '$(ASFNetFramework)' != ''">
-    <TargetFrameworks>netcoreapp2.2;net48</TargetFrameworks>
+    <TargetFrameworks>netcoreapp3.0;net48</TargetFrameworks>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(OS)' != 'Windows_NT' AND '$(ASFNetFramework)' == ''">
-    <TargetFramework>netcoreapp2.2</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)' == 'Release'">

ArchiSteamFarm.CustomPlugins.ExamplePlugin/CatAPI.cs

@@ -20,7 +20,6 @@
 // limitations under the License.
 
 using System;
-using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Newtonsoft.Json;
@@ -51,7 +50,7 @@ namespace ArchiSteamFarm.CustomPlugins.ExamplePlugin {
 			return Uri.EscapeUriString(response.Content.Link);
 		}
 
-		[SuppressMessage("ReSharper", "ClassCannotBeInstantiated")]
+		[System.Diagnostics.CodeAnalysis.SuppressMessage("ReSharper", "ClassCannotBeInstantiated")]
 		private sealed class MeowResponse {
 #pragma warning disable 649
 			[JsonProperty(PropertyName = "file", Required = Required.Always)]

ArchiSteamFarm.CustomPlugins.ExamplePlugin/nuget.config

@@ -1,11 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-
-<configuration>
-	<config>
-		<add key="dependencyversion" value="Highest" />
-	</config>
-
-	<packageSources>
-		<add key="dotnet-core" value="https://dotnet.myget.org/F/dotnet-core/api/v3/index.json" />
-	</packageSources>
-</configuration>