chore(package): update ts-jest to version 26.0.0

Closes #22

Author: greenkeeper[bot]

package.json

@@ -41,7 +41,7 @@
     "eslint-plugin-standard": "^4.0.1",
     "jest": "^24.9.0",
     "rollup-plugin-typescript2": "^0.21.0",
-    "ts-jest": "^24.2.0",
+    "ts-jest": "^26.0.0",
     "typescript": "^3.7.3",
     "vuepress": "^1.2.0"
   }