Use GitHub Action: japgolly/setup-everything-scala

Which makes use of the brand new GitHub Actions feature: action
composition. This allows us to just have a single GHA for everything
Scala and Scala.JS, and centralise and hide boring details like caching.

Author: japgolly

.github/workflows/ci.yml

@@ -23,10 +23,9 @@ jobs:
     steps:
 
       - uses: actions/checkout@v2
-      - uses: olafurpg/setup-scala@v13
-        with:
-          java-version: "adopt@1.8"
-      - uses: coursier/cache-action@v6
+
+      - name: Setup Scala
+        uses: japgolly/setup-everything-scala@v1.0
 
       - name: Hacks for Scala 2.10
         if: matrix.scalaversion == '2.10.7'
@@ -52,9 +51,6 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - uses: olafurpg/setup-scala@v13
-        with:
-          java-version: "adopt@1.8"
-      - uses: coursier/cache-action@v6
+      - uses: japgolly/setup-everything-scala@v1.0
       - name: Readme generation
         run: sbt readme/run

.github/workflows/ghpages.yml

@@ -11,10 +11,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - uses: olafurpg/setup-scala@v13
-        with:
-          java-version: "adopt@1.8"
-      - uses: coursier/cache-action@v6
+
+      - name: Setup Scala
+        uses: japgolly/setup-everything-scala@v1.0
 
       - name: Build
         run: sbt readme/run

.github/workflows/release.yml

@@ -12,13 +12,19 @@ jobs:
     env:
       SCALAJS_VERSION: "${{ matrix.scalajsversion == '0.6.x' && '0.6.28' || '' }}"
     steps:
+
       - uses: actions/checkout@v2
         with:
           fetch-depth: 0
-      - uses: olafurpg/setup-scala@v13
+
+      - name: Setup Scala
+        uses: japgolly/setup-everything-scala@v1.0
+
       - name: Hacks for Scala 2.10
         run: ./prepareForScala210.sh
-      - run: sbt ci-release
+
+      - name: Release
+        run: sbt ci-release
         env:
           PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
           PGP_SECRET: ${{ secrets.PGP_SECRET }}