Automatically publish documentation on pursuit (#6)

This requires a `GITHUB_TOKEN` environment variable to be set (in travis). This token was obtained by following the instructions printed by `purs login`.

`sudo: required` makes stuff *a lot* faster. We don't actually require sudo.

.travis.yml

@@ -1,10 +1,16 @@
 language: node_js
 node_js: node
 dist: trusty
-sudo: false
+sudo: required
 install:
   - npm install -g bower purescript pulp
-script:
   - npm install pouchdb
+script:
+  - bower install --production
+  - pulp build
   - bower install
   - pulp test
+after_success:
+  - test $TRAVIS_TAG &&
+    echo $GITHUB_TOKEN | pulp login &&
+    echo y | pulp publish --no-push