chore(package): update rollup to version 2.2.0

Closes #37

Author: greenkeeper[bot]

package.json

@@ -47,7 +47,7 @@
     "nock": "^11.3.5",
     "prettier": "^1.14.2",
     "rimraf": "^3.0.0",
-    "rollup": "^1.27.7",
+    "rollup": "^2.2.0",
     "rollup-plugin-sourcemaps": "^0.4.2",
     "ts-jest": "^23.1.4",
     "typescript": "^2.9.2",