Update prettier to version 2.0.2

Author: depfu[bot]

package.json

@@ -70,7 +70,7 @@
     "mocha-lcov-reporter": "^1.3.0",
     "nyc": "^15.0.0",
     "offline-github-changelog": "^1.2.0",
-    "prettier": "~1.19.1",
+    "prettier": "~2.0.2",
     "rollup": "^2.0.2",
     "rollup-plugin-commonjs": "^10.0.0",
     "rollup-plugin-json": "^4.0.0",