Tell npm to use known registrars on travis

npm no longer supports its self-signed certificate [1], so instead we tell
it to use the default (browser-like) set of certificates from the
operating system.

[1] http://blog.npmjs.org/post/78085451721/npms-self-signed-certificate-is-no-more

Closes #347
Update pagination documentation

Updated to include details on the various properties that are included
on paginated result pages. Also added some example JSON.
Merge pull request #348 from mysociety/pagination-documentation

Update pagination documentation
Update popit-api to latest master

Includes the following features/fixes:

- Added `include_root` parameter to API listing pages
- Pagination metadata such as total results page no. etc
deploy to production - version bump to 0.0.27
Merge branch 'master' into production