chore(deps): add eslint@6 to peerDependencies (#22)

Author: azu

package.json

@@ -32,10 +32,10 @@
     "textlint"
   ],
   "devDependencies": {
-    "eslint": "5.6.1",
+    "eslint": "6.0.1",
     "textlint-scripts": "^2.1.0"
   },
   "peerDependencies": {
-    "eslint": "^3.0.0 || ^4.0.0 || ^5.0.0"
+    "eslint": "^3.0.0 || ^4.0.0 || ^5.0.0 || ^6.0.0"
   }
 }