Bump minimum Node.js version to 10.x (#122)

In a subsequent patch #120, we bump eslint-config-wikimedia to
0.17.0, which also requires bumping eslint to 7.9.0 which drops
support for Node.js 8.x

Bug: T266462

.github/workflows/node.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-v: [8.x, 10.x, 12.x]
+        node-v: [10.x, 12.x]
     steps:
       - name: Checkout
         uses: actions/checkout@v2