GitHub CI with build badge. (#215)

Closes #213

.github/workflows/build.yml

@@ -0,0 +1,21 @@
+# This workflow will build a Java project with Maven
+# For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-maven
+
+name: Java CI with Maven
+
+on: [ push, pull_request ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up JDK 8
+        uses: actions/setup-java@v2
+        with:
+          java-version: '8'
+          distribution: 'adopt'
+          cache: maven
+      - name: Build with Maven
+        run: mvn --batch-mode --update-snapshots verify

README.md

@@ -1,6 +1,6 @@
 # Spatial4j
 
-[![Build](https://travis-ci.org/locationtech/spatial4j.svg)](https://travis-ci.org/locationtech/spatial4j)
+[![Build](https://github.com/locationtech/spatial4j/actions/workflows/build.yml/badge.svg)](ttps://github.com/locationtech/spatial4j/actions)
 [![Coverage](https://img.shields.io/codecov/c/github/locationtech/spatial4j.svg)](https://codecov.io/github/locationtech/spatial4j/)
 [![Maven](https://img.shields.io/maven-central/v/org.locationtech.spatial4j/spatial4j.svg)](https://maven-badges.herokuapp.com/maven-central/org.locationtech.spatial4j/spatial4j/)