fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:ecstatic:20151223

Latest report for d2s/koodiklinikka.fi:
https://snyk.io/test/github/d2s/koodiklinikka.fi

package.json

@@ -21,7 +21,7 @@
     "axios": "^0.4.2",
     "classnames": "^2.2.1",
     "font-awesome": "^4.4.0",
-    "http-server": "^0.8.0",
+    "http-server": "^0.9.0",
     "lodash": "^3.9.1",
     "parse-github-event": "^0.2.0",
     "prop-types": "^15.5.10",