Fix node version variable in CI workflow

Author: jonaskello

.github/workflows/ci.yml

@@ -42,10 +42,10 @@ jobs:
     steps:
       - uses: actions/checkout@v1
 
-      - name: Use Node.js ${{ matrix.node-version }}
+      - name: Use Node.js ${{ matrix.node_version }}
         uses: actions/setup-node@v1
         with:
-          node-version: ${{ matrix.node-version }}
+          node-version: ${{ matrix.node_version }}
 
       - name: yarn install
         run: yarn install --frozen-lockfile