companion: add necessary devDependencies for isolated build

package.json

@@ -83,7 +83,7 @@
     "@types/lodash.merge": "^4.6.3",
     "@types/morgan": "^1.7.35",
     "@types/ms": "^0.7.30",
-    "@types/node": "^8.5.1",
+    "@types/node": "^12.6.8",
     "@types/react": "^16.8.10",
     "@types/request": "^2.0.9",
     "@types/tus-js-client": "^1.4.1",

packages/@uppy/companion/package.json

@@ -64,6 +64,10 @@
     "validator": "^9.0.0",
     "ws": "1.1.5"
   },
+  "devDependencies": {
+    "@types/node": "^12.6.8",
+    "typescript": "^3.4.5"
+  },
   "files": [
     "bin/",
     "lib/"