fix(param-names): avoid including fixable: code when not fixable

Per the eslint docs at https://eslint.org/docs/developer-guide/working-with-rules#options-schemas

> Omit the fixable property if the rule is not fixable.

Author: brettz9

rules/param-names.js

@@ -6,8 +6,7 @@ module.exports = {
   meta: {
     docs: {
       url: getDocsUrl('param-names')
-    },
-    fixable: 'code'
+    }
   },
   create(context) {
     return {