remove dev dependencies; rely on automatic install

Author: feross

.travis.yml

@@ -1,3 +1,5 @@
 language: node_js
 node_js:
   - lts/*
+before_install:
+  - npm i -g npm@7

package.json

@@ -11,11 +11,6 @@
     "url": "https://github.com/standard/eslint-config-standard/issues"
   },
   "devDependencies": {
-    "eslint": "^7.11.0",
-    "eslint-plugin-import": "^2.22.1",
-    "eslint-plugin-node": "^11.1.0",
-    "eslint-plugin-promise": "^4.2.1",
-    "eslint-plugin-standard": "^4.0.2",
     "tape": "^5.0.1"
   },
   "homepage": "https://github.com/standard/eslint-config-standard",