Tell npm to use known registrars on travis
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

mysociety/popit,Sinar/popit,Sinar/popit,Sinar/popit,mysociety/popit,openstate/popit,mysociety/popit,Sinar/popit,openstate/popit,openstate/popit,openstate/popit,mysociety/popit,mysociety/popit