chore(package): update tsutils to version 2.26.0

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
     "semantic-release": "^12.2.2",
     "ts-jest": "^22.0.1",
     "tslint": "^5.9.1",
-    "tsutils": "^2.18.0",
+    "tsutils": "^2.26.0",
     "typedoc": "^0.10.0",
     "typescript": "^2.6.2"
   },