Bump subscriptions-transport-ws from 0.9.18 to 0.9.19 (#7106)

Bumps [subscriptions-transport-ws](https://github.com/apollostack/subscriptions-transport-ws) from 0.9.18 to 0.9.19.
- [Release notes](https://github.com/apollostack/subscriptions-transport-ws/releases)
- [Changelog](https://github.com/apollographql/subscriptions-transport-ws/blob/master/CHANGELOG.md)
- [Commits](https://github.com/apollostack/subscriptions-transport-ws/commits)

---
updated-dependencies:
- dependency-name: subscriptions-transport-ws
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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package.json

@@ -100,7 +100,7 @@
     "pdfjs-dist": "2.5.207",
     "raphael": "2.3.0",
     "rxjs": "^6.6.3",
-    "subscriptions-transport-ws": "^0.9.18",
+    "subscriptions-transport-ws": "^0.9.19",
     "tslib": "^2.3.0",
     "zone.js": "~0.10.2"
   },