Set minimum Atom version

Arcanemagus · Arcanemagus · commit a16268014b5b · 2016-10-31T13:52:06.000-07:00
Atom has only supported the configSchema since v1.4.0.
diff --git a/package.json b/package.json
@@ -19,6 +19,9 @@
       "default": false
     }
   },
+  "engines": {
+    "atom": ">=1.4.0 <2.0.0"
+  },
   "dependencies": {
     "atomlinter-csslint": "0.10.0",
     "atom-linter": "^8.0.0",
