ci(travis): Make Travis actually run the tests (facepalm).

ad42abd sets `script` in `.travis.yml`
to `npm run transpile`, without realising that the implicit default of
`npm test` will be overriden and thus no longer run.

.travis.yml

@@ -1,5 +1,7 @@
 language: node_js
-script: npm run transpile
+script:
+  - npm run transpile
+  - npm test
 node_js:
   - "node"
   - "6"

CHANGELOG.md

@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 - Unified testing/coverage commands into a single `npm test`.
 
+### Fixed
+- Restore running of tests on Travis CI (broken since ad42abd532d1628c75b6f9bddeca36181c3846a3).
+
 ## [1.2.3] - 2017-08-07
 ### Added
 - Add a copy of the most recent tests results to `tests/`.