chore(package): update ts-jest to version 26.1.0

Closes #23

Author: greenkeeper[bot]

package.json

@@ -40,7 +40,7 @@
     "jest": "^23.6.0",
     "prettier": "^1.14.3",
     "semantic-release": "^17.0.1",
-    "ts-jest": "^24.0.0",
+    "ts-jest": "^26.1.0",
     "tslint": "^5.11.0",
     "typescript": "^3.1.5"
   },