Clarify which Node versions are supported

See #166

Author: sgravrock

.travis.yml

@@ -1,8 +1,9 @@
 sudo: false
 language: node_js
+# NOTE: When changing the list of Node versions, be sure to update `engines`
+# in package.json as well as setup/nodejs.md in the docs repo.
 node_js:
   - '14'
-  - '13'
   - '12'
   - '10'
 before_script:

package.json

@@ -31,6 +31,9 @@
     "shelljs": "^0.8.3",
     "slash": "^3.0.0"
   },
+  "engines": {
+    "node": "^10 || ^12 || ^14"
+  },
   "eslintConfig": {
     "parserOptions": {
       "ecmaVersion": 11