chore: add GH Actions CI (#323)

.gitattributes

@@ -0,0 +1 @@
+* text=auto eol=lf

.github/workflows/nodejs.yml

@@ -0,0 +1,23 @@
+name: Node.js CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: Test on Node.js v${{ matrix.node-version }} and OS ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        node-version: [10.x, 12.x, 13.x]
+        os: [ubuntu-latest, windows-latest, macOS-latest]
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+      - name: Install and test
+        run: npm it

README.md

@@ -1,4 +1,4 @@
-# Prometheus client for node.js [![Build Status](https://travis-ci.org/siimon/prom-client.svg?branch=master)](https://travis-ci.org/siimon/prom-client) [![Build status](https://ci.appveyor.com/api/projects/status/k2e0gwonkcee3lp9/branch/master?svg=true)](https://ci.appveyor.com/project/siimon/prom-client/branch/master)
+# Prometheus client for node.js [![Build Status](https://travis-ci.org/siimon/prom-client.svg?branch=master)](https://travis-ci.org/siimon/prom-client) [![Build status](https://ci.appveyor.com/api/projects/status/k2e0gwonkcee3lp9/branch/master?svg=true)](https://ci.appveyor.com/project/siimon/prom-client/branch/master) [![Actions Status](https://github.com/siimon/prom-client/workflows/Node.js%20CI/badge.svg?branch=master)](https://github.com/siimon/prom-client/actions)
 
 A prometheus client for node.js that supports histogram, summaries, gauges and
 counters.