fix: move express to peerDependencies

Author: azu

package.json

@@ -64,9 +64,10 @@
     "supertest": "^6.1.3",
     "ts-node": "^9.1.1",
     "ts-node-test-register": "^9.0.1",
-    "typescript": "^4.1.3"
-  },
-  "dependencies": {
+    "typescript": "^4.1.3",
     "express": "^4.17.1"
+  },
+  "peerDependencies": {
+    "express": "^4.0.0"
   }
 }