types: stick with ts version that works with version of eslint

package.json

@@ -41,7 +41,7 @@
     "@polkadot/rpc-provider": "2.4.1",
     "@polkadot/metadata": "2.4.1",
     "babel-core": "^7.0.0-bridge.0",
-    "typescript": "^4.1.3",
+    "typescript": "^3.9.7",
     "bn.js": "^5.1.2",
     "@dzlzv/hydra-indexer-lib": "0.0.21-legacy.1.26.1"
   },

yarn.lock

@@ -25590,10 +25590,10 @@ typescript-formatter@^7.2.2:
     commandpost "^1.0.0"
     editorconfig "^0.15.0"
 
-typescript@^3.0.3, typescript@^3.8.3, typescript@^3.9.5, typescript@^3.9.6, typescript@^3.9.7, typescript@^4.0.3, typescript@^4.1.3:
-  version "4.1.3"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-4.1.3.tgz#519d582bd94cba0cf8934c7d8e8467e473f53bb7"
-  integrity sha512-B3ZIOf1IKeH2ixgHhj6la6xdwR9QrLC5d1VKeCSY4tvkqhF2eqd9O7txNlS0PO3GrBAFIdr3L1ndNwteUbZLYg==
+typescript@^3.0.3, typescript@^3.8.3, typescript@^3.9.5, typescript@^3.9.6, typescript@^3.9.7, typescript@^4.0.3:
+  version "3.9.7"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.9.7.tgz#98d600a5ebdc38f40cb277522f12dc800e9e25fa"
+  integrity sha512-BLbiRkiBzAwsjut4x/dsibSTB6yWpwT5qWmC2OfuCg3GgVQCSgMs4vEctYPhsaGtd0AeuuHMkjZ2h2WG8MSzRw==
 
 ua-parser-js@^0.7.18:
   version "0.7.23"