fix: fix build babel

Author: iamkun

.babelrc

@@ -13,9 +13,6 @@
             "modules": false
           }
         ]
-      ],
-      "plugins": [
-        "external-helpers"
       ]
     }
   }

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "test": "jest",
     "lint": "echo start lint && ./node_modules/.bin/eslint src/* test/*",
-    "build": "rollup -c"
+    "build": "BABEL_ENV=build rollup -c"
   },
   "pre-commit": [
     "lint"

src/index.js

@@ -173,10 +173,10 @@ class Dayjs {
   daysInMonth() {
     return new Dayjs(new Date(this.year(), this.month() + 1, 0)).date()
   }
-}
 
-export default (config) => {
-  const d = new Dayjs(config)
-  d.clone = () => new Dayjs(d)
-  return d
+  clone() {
+    return new Dayjs(this)
+  }
 }
+
+export default config => (new Dayjs(config))