fix: move serve-static @types to normal dependencies

Consumers of this library need those @types packages to be installed, which
won't happen if they are in devDependencies

Fixes #1917 ... again

packages/rest/package.json

@@ -27,8 +27,10 @@
     "@loopback/openapi-v3-types": "^1.0.0",
     "@types/cors": "^2.8.3",
     "@types/express": "^4.11.1",
+    "@types/express-serve-static-core": "^4.16.0",
     "@types/http-errors": "^1.6.1",
     "@types/parseurl": "^1.3.1",
+    "@types/serve-static": "1.13.2",
     "ajv": "^6.5.1",
     "body": "^5.1.0",
     "cors": "^2.8.4",
@@ -52,11 +54,9 @@
     "@loopback/repository": "^1.0.2",
     "@loopback/testlab": "^1.0.0",
     "@types/debug": "0.0.30",
-    "@types/express-serve-static-core": "^4.16.0",
     "@types/js-yaml": "^3.11.1",
     "@types/lodash": "^4.14.106",
     "@types/node": "^10.11.2",
-    "@types/serve-static": "1.13.2",
     "@types/qs": "^6.5.1",
     "@types/type-is": "^1.6.2"
   },