rebuild gh-pages per PR

.travis.yml

@@ -1,3 +1,10 @@
 language: dart
 script: dart -c tool/grind.dart
 sudo: false
+
+after_success:
+  - test $TRAVIS_PULL_REQUEST == "false" && test $TRAVIS_BRANCH == "master" && bash tool/ghpages.sh
+
+env:
+  global:
+  - secure: LImP9GVVlazcPAwId9YewKxtW7fJKYex6Nt02uUzXKSY6Dx7Rn5jXp5afUwnSYs1zMJIb3PJUnzRkWobRF7xShZhAw41D1yNRQrTgoM3OaPCCPUWRzv9M5rBdiPIbw3iP5kFwOYTLjeApX3d+OHUw6jUyPu0fCyvootVPIi+jYE=

tool/ghpages.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+set -o errexit -o nounset
+
+rev=$(git rev-parse --short HEAD)
+
+cd doc/api
+
+git init
+git config user.name "Devon Carew"
+git config user.email "devoncarew@google.com"
+
+git remote add upstream "https://$GH_TOKEN@github.com/google/grinder.dart.git"
+git fetch upstream
+git reset upstream/gh-pages
+
+touch .
+
+git add -A .
+git commit -m "rebuild pages at ${rev}"
+git push -q upstream HEAD:gh-pages