Update dev dependencies to latest

- `eslint` to `^7.11.0`
- `mocha` to `^8.1.3`
- `typescript` to `^4.0.3`

Signed-off-by: Miroslav Bajtoš <mbajtoss@gmail.com>

package.json

@@ -39,13 +39,13 @@
     "async-iterators": "^0.2.2",
     "bson": "^4.0.1",
     "coveralls": "^3.0.1",
-    "eslint": "^6.7.2",
+    "eslint": "^7.11.0",
     "eslint-config-loopback": "^13.0.0",
     "loopback-connector-throwing": "file:./test/fixtures/loopback-connector-throwing",
-    "mocha": "^7.1.1",
+    "mocha": "^8.1.3",
     "nyc": "^15.0.0",
     "should": "^13.2.3",
-    "typescript": "^3.2.2"
+    "typescript": "^4.0.3"
   },
   "dependencies": {
     "async": "^3.1.0",