chore(package): update typescript to version 2.6.1

Closes #9

Author: greenkeeper[bot]

package.json

@@ -55,7 +55,7 @@
     "semantic-release": "^6.3.6",
     "ts-node": "~3.3.0",
     "tslint": "~5.5.0",
-    "typescript": "~2.4.1"
+    "typescript": "~2.6.1"
   },
   "repository": {
     "type": "git",