chore(node_modules): lock koa-router version

The ownership of the koa-router package was transferred to an "unknown"
user.

See more on Github: nodejs/package-maintenance#77,
Hacker News: https://news.ycombinator.com/item?id=19156707 and the npm
blog: https://blog.npmjs.org/post/182828408610/the-security-risks-of-changing-package-owners

garden-service/package.json

@@ -63,7 +63,7 @@
     "koa": "^2.6.2",
     "koa-bodyparser": "^4.2.1",
     "koa-mount": "^4.0.0",
-    "koa-router": "^7.4.0",
+    "koa-router": "7.4.0",
     "koa-static": "^5.0.0",
     "koa-websocket": "^5.0.1",
     "lodash": "^4.17.11",
@@ -115,7 +115,7 @@
     "@types/koa": "^2.0.47",
     "@types/koa-bodyparser": "^4.2.1",
     "@types/koa-mount": "^3.0.1",
-    "@types/koa-router": "^7.0.35",
+    "@types/koa-router": "7.0.35",
     "@types/koa-websocket": "^5.0.3",
     "@types/lodash": "^4.14.119",
     "@types/log-symbols": "^2.0.0",