Revert "Run workflows with Node.js 14 (#23)"

GitHub JavaScript actions run with Node.js 12.

https://docs.github.com/en/actions/creating-actions/creating-a-javascript-action#prerequisites

This reverts commit a5edb65.

Author: joschi

.github/workflows/test-nightly.yml

@@ -19,10 +19,10 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v2
-    - name: Set Node.js 14.x
+    - name: Set Node.js 12.x
       uses: actions/setup-node@v1
       with:
-        node-version: 14.x
+        node-version: 12.x
     - name: npm install
       run: npm install
     - name: Clear tool cache

.github/workflows/workflow.yml

@@ -18,10 +18,10 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v2
-    - name: Setup Node.js 14
+    - name: Setup Node.js 12
       uses: actions/setup-node@v1
       with:
-        node-version: 14.x
+        node-version: 12.x
     - name: npm install
       run: npm install
     - name: Lint