Update peer dependency to typescript 4.0+

Author: Igorbek

package.json

@@ -21,7 +21,7 @@
     },
     "typings": "dist/index.d.ts",
     "peerDependencies": {
-        "typescript": "^2.5.2 || ^3.0"
+        "typescript": "^2.5.2 || ^3.0 || ^4.0"
     },
     "devDependencies": {
         "@types/jest": "^25.2.1",