Bump serve from 6.4.9 to 7.1.3

Bumps [serve](https://github.com/zeit/serve) from 6.4.9 to 7.1.3.
- [Release notes](https://github.com/zeit/serve/releases)
- [Commits](https://github.com/zeit/serve/compare/6.4.9...7.1.3)

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -38,7 +38,7 @@
     "nyc": "^11.4.1",
     "opn-cli": "^3.1.0",
     "prettier": "^1.14.3",
-    "serve": "^6.4.4",
+    "serve": "^7.1.3",
     "tap-nyc": "^1.0.3",
     "tap-spec": "^4.1.1",
     "tape": "^4.8.0",