replace Travis-CI with GitHub Actions

and also:

* upgrade to Scala 2.13.6 (was 2.13.4)
* upgrade to sbt-scala-module 3.0.0 (was 2.4.0)
* add JDK 17 to crossbuild

Author: SethTisue

.github/workflows/ci.yml

@@ -0,0 +1,25 @@
+name: test
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [8, 11, 17]
+        scala: [2.13.6]
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - uses: coursier/cache-action@v6
+    - uses: actions/setup-java@v2
+      with:
+        distribution: adopt
+        java-version: ${{matrix.java}}
+    - name: Test
+      run: sbt ++${{matrix.scala}} test package

.github/workflows/release.yml

@@ -0,0 +1,21 @@
+name: Release
+on:
+  push:
+    tags: ["*"]
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: actions/setup-java@v2
+        with:
+          distribution: adopt
+          java-version: 8
+      - run: sbt versionCheck ci-release
+        env:
+          PGP_PASSPHRASE: ${{secrets.PGP_PASSPHRASE}}
+          PGP_SECRET: ${{secrets.PGP_SECRET}}
+          SONATYPE_PASSWORD: ${{secrets.SONATYPE_PASSWORD}}
+          SONATYPE_USERNAME: ${{secrets.SONATYPE_USERNAME}}

.travis.yml

@@ -1,3 +1,5 @@
+ThisBuild / scalaVersion := "2.13.6"
+
 lazy val root = project.in(file("."))
   .aggregate(scalaLibraryNextJVM, scalaLibraryNextJS)
   .settings(

build.sbt

@@ -1,3 +1,3 @@
-addSbtPlugin("org.scala-lang.modules" % "sbt-scala-module" % "2.4.0")
+addSbtPlugin("org.scala-lang.modules" % "sbt-scala-module" % "3.0.0")
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.7.0")
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "1.1.0")