ci: run tests against eslint@7 (#572)

Author: G-Rath

.github/workflows/nodejs.yml

@@ -19,7 +19,11 @@ jobs:
       fail-fast: false
       matrix:
         node-version: [8.x, 10.x, 12.x, 13.x]
-        eslint-version: [5, 6]
+        eslint-version: [5, 6, 7]
+        exclude:
+          # eslint@7 doesn't support node@8
+          - node-version: 8.x
+            eslint-version: 7
     runs-on: ubuntu-latest
 
     steps: