ci: replace travis with actions

Author: rvagg

.github/workflows/main.yml

@@ -0,0 +1,29 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest] # windows-latest needs openssl installed in C:\OpenSSL-Win64\
+        node-version: [10.x, 12.x, 13.x]
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v1
+      with:
+        fetch-depth: 1
+
+    - name: Install and test with Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm install
+    - run: npm run build --if-present
+    - run: npm test
+      env:
+        CI: true

.travis.yml

@@ -1,8 +1,7 @@
 bignum
 ======
 
-[![Travis build status](https://travis-ci.org/justmoon/node-bignum.svg?branch=master)](https://travis-ci.org/justmoon/node-bignum)
-[![AppVeyor build status](https://ci.appveyor.com/api/projects/status/svyho17a4eq2f0a7/branch/master?svg=true)](https://ci.appveyor.com/project/RodVagg/node-bignum/branch/master)
+[![Build Status](https://github.com/justmoon/node-bignum/workflows/CI/badge.svg)](https://github.com/justmoon/node-bignum/actions?workflow=CI)
 
 Arbitrary precision integral arithmetic for Node.js using
 OpenSSL.