Move to GH Actions (sky-ecosystem#235)

* Move to GH Actions

* Pin Nix version to 2.3.6

* Run CI actions on all branches and PRs

Co-authored-by: grandizzy <grandizzy@localhost>

Author: dizzy

.github/workflows/tests.yaml

@@ -0,0 +1,24 @@
+on: [push, pull_request]
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout repository and submodules
+      uses: actions/checkout@v2
+      with:
+        submodules: recursive
+
+    - name: Install nix 2.3.6
+      uses: cachix/install-nix-action@v13
+      with:
+        install_url: https://releases.nixos.org/nix/nix-2.3.6/install
+        nix_path: nixpkgs=channel:nixos-unstable
+
+    - name: Use maker cachix
+      uses: cachix/cachix-action@v10
+      with:
+        name: maker
+
+    - name: Run tests
+      run: nix-shell --pure --run 'dapp test'

.travis.yml

@@ -1,6 +1,5 @@
 # Multi Collateral Dai
-[![Build Status](https://travis-ci.com/makerdao/dss.svg?branch=master)](https://travis-ci.com/makerdao/dss)
-[![codecov](https://codecov.io/gh/makerdao/dss/branch/master/graph/badge.svg)](https://codecov.io/gh/makerdao/dss)
+![Build Status](https://github.com/makerdao/dss/actions/workflows/.github/workflows/tests.yaml/badge.svg?branch=master)
 
 This repository contains the core smart contract code for Multi
 Collateral Dai. This is a high level description of the system, assuming