chore(package): update rollup to version 1.21.2

Closes #55

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "coveralls": "3.0.3",
     "jest": "24.1.0",
     "rimraf": "2.6.3",
-    "rollup": "1.3.3",
+    "rollup": "1.21.2",
     "rollup-plugin-cleanup": "^3.1.1",
     "ts-jest": "24.0.1",
     "tslint": "5.13.0",