Pin @types/express-serve-static-core version to 4.17.0

as later patch versions introduce string interpolations that are not recognized
by typescript v3.

Upgrading typescript is another option, however, that introduce incompatibility
with tslint.

Author: jeremymeng

package.json

@@ -66,7 +66,8 @@
     "@microsoft/api-extractor": "^7.18.11",
     "@ts-common/azure-js-dev-tools": "^19.4.0",
     "@types/chai": "^4.1.7",
-    "@types/express": "^4.17.0",
+    "@types/express": "4.17.0",
+    "@types/express-serve-static-core": "4.17.0",
     "@types/fetch-mock": "^7.3.1",
     "@types/form-data": "^2.2.1",
     "@types/glob": "^7.1.1",