Update typescript version (#657)

Author: Zedwag

packages/devextreme-react-generator/package.json

@@ -39,6 +39,6 @@
     "del-cli": "^3.0.1",
     "jest": "^24.8.0",
     "ts-jest": "^24.0.2",
-    "typescript": "^3.9.7"
+    "typescript": "~4.2"
   }
 }

packages/devextreme-react/package.json

@@ -49,7 +49,7 @@
     "gulp-shell": "^0.6.5",
     "gulp-typescript": "^5.0.0",
     "ts-jest": "^24.0.2",
-    "typescript": "^3.9.7",
+    "typescript": "~4.2",
     "@testing-library/react": "^11.2.5",
     "@testing-library/user-event": "^13.0.1"
   },

packages/sandbox/package.json

@@ -22,7 +22,7 @@
     "style-loader": "^0.23.1",
     "ts-loader": "^5.3.3",
     "tsconfig-paths-webpack-plugin": "^3.3.0",
-    "typescript": "^3.9.7",
+    "typescript": "~4.2",
     "url-loader": "^0.6.2",
     "webpack": "^4.29.2",
     "webpack-cli": "^3.2.3",