drop travis config for CI builds (#2067)

.github/workflows/netcore.yml

@@ -1,4 +1,4 @@
-name: Build and test with .NET Core
+name: CI Build
 
 on:
   pull_request:

.travis.yml

@@ -1,26 +0,0 @@
-language: csharp
-
-notifications:
-  email: false
-
-matrix:
-  include:
-    - os: linux
-      dist: xenial
-      sudo: required
-      dotnet: 2.2
-    - os: osx
-      osx_image: xcode8.3
-      dotnet: 2.2.402
-
-branches:
-  only:
-    - "master"
-
-before_script:
-  - if test "$TRAVIS_OS_NAME" == "osx"; then export FrameworkPathOverride=/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.5/; else export FrameworkPathOverride=/usr/lib/mono/4.5/; fi
-
-script:
-  - git fetch --unshallow --tags
-  # disengage core only switch because mono ships .NETFramework targets
-  - ./build.sh --coreonly=false --linksources=true --verbosity=verbose

README.md

@@ -1,7 +1,7 @@
 # Octokit - GitHub API Client Library for .NET 
 
+![Build status](https://github.com/octokit/octokit.net/workflows/CI%20Build/badge.svg)
 [![Build status](https://ci.appveyor.com/api/projects/status/cego2g42yw26th26/branch/master?svg=true)](https://ci.appveyor.com/project/github-windows/octokit-net/branch/master)
-[![Build Status]( https://travis-ci.org/octokit/octokit.net.svg)]( https://travis-ci.org/octokit/octokit.net)
 [![codecov](https://codecov.io/gh/octokit/octokit.net/branch/master/graph/badge.svg)](https://codecov.io/gh/octokit/octokit.net)
 [![Join the chat at https://gitter.im/octokit/octokit.net](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/octokit/octokit.net?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![NuGet](http://img.shields.io/nuget/v/Octokit.svg)](https://www.nuget.org/packages/Octokit)