Tweak dependencies, CI

* Bump dependencies

* Upgrade tap

Use tap's nyc integration.

* Use Node.js 10 type definitions for observable compatibility

* Only build master and version branches, rely on pull requests otherwise

Author: novemberborn

.travis.yml

@@ -1,3 +1,7 @@
+branches:
+  only:
+    - master
+    - /v\d.+/
 language: node_js
 os:
   - windows