chore(CI): migrate to github actions

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+on:
+  push:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 6 * * 1"
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+        crystal:
+          - latest
+          - nightly
+          - 1.0.0
+    runs-on: ${{ matrix.os }}
+    container: crystallang/crystal:${{ matrix.crystal }}-alpine
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install dependencies
+      run: shards install --ignore-crystal-version
+    - name: Lint
+      run: ./bin/ameba
+    - name: Format
+      run: crystal tool format --check
+    - name: Run tests
+      run: crystal spec -v --error-trace

README.md

@@ -1,6 +1,6 @@
 # Crystal Lang S2 Cells
 
-[![Build Status](https://travis-ci.com/spider-gazelle/s2_cells.svg?branch=master)](https://travis-ci.com/github/spider-gazelle/s2_cells)
+[![CI](https://github.com/spider-gazelle/s2_cells/actions/workflows/ci.yml/badge.svg)](https://github.com/spider-gazelle/s2_cells/actions/workflows/ci.yml)
 
 Maps Lat Lon coordinates to S2 Cells.
 Useful for things like storing points [in InfluxDB](https://docs.influxdata.com/influxdb/v2.0/reference/flux/stdlib/experimental/geo/#geo-schema-requirements)