Update dependency jest to v26 (#18)

Co-authored-by: Renovate Bot <[email protected]>

Author: renovate[bot]

package.json

@@ -21,7 +21,7 @@
     "@types/graphql": "14.5.0",
     "@types/node": "14.0.13",
     "graphql-schema-typescript": "1.3.2",
-    "jest": "21.2.1",
+    "jest": "26.0.1",
     "serverless": "1.72.0",
     "serverless-dotenv-plugin": "2.4.2",
     "serverless-offline": "6.4.0",