add jest types

Author: developit

package.json

@@ -106,6 +106,7 @@
   "devDependencies": {
     "@babel/core": "^7.2.2",
     "@babel/preset-env": "^7.1.6",
+    "@types/jest": "^26.0.24",
     "babel-jest": "^24.1.0",
     "babel-preset-env": "^1.7.0",
     "eslint": "^5.2.0",