chore(package): update rollup-plugin-typescript2 to version 0.21.1

Closes #26

Author: greenkeeper[bot]

package.json

@@ -31,7 +31,7 @@
     "rollup": "^0.65.0",
     "rollup-plugin-commonjs": "^9.0.0",
     "rollup-plugin-node-resolve": "^3.0.0",
-    "rollup-plugin-typescript2": "^0.14.0",
+    "rollup-plugin-typescript2": "^0.21.1",
     "semver": "^5.4.1",
     "ts-jest": "^23.0.0",
     "typescript": "^2.6.2"