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

Closes #35

Author: greenkeeper[bot]

package.json

@@ -49,7 +49,7 @@
     "rimraf": "^3.0.0",
     "rollup": "^1.27.7",
     "rollup-plugin-sourcemaps": "^0.4.2",
-    "ts-jest": "^23.1.4",
+    "ts-jest": "^26.1.0",
     "typescript": "^2.9.2",
     "uglify-js": "^3.4.8"
   },