chore: add changelog script

Author: yyx990803

package.json

@@ -8,7 +8,8 @@
     "url": "git@github.com:vuejs/vue-style-loader.git"
   },
   "scripts": {
-    "test": "jest"
+    "test": "jest",
+    "prepublishOnly": "conventional-changelog -p angular -r 2 -i CHANGELOG.md -s"
   },
   "license": "MIT",
   "dependencies": {
@@ -19,6 +20,7 @@
     "babel-core": "^6.26.0",
     "babel-jest": "^22.1.0",
     "babel-plugin-transform-es2015-modules-commonjs": "^6.26.0",
+    "conventional-changelog-cli": "^2.0.1",
     "jest": "^22.1.4"
   }
 }