increase version for segwit

Reviewers: mark, robert, benchan

Reviewed By: benchan

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D6277

update docs, get environment from shell

Summary:
update docs on starting bitgoexpress
get bitgo environment from shell variable BITGO_ENV
put an example browser.html to show how to include sdk into browser side app

Reviewers: ryan

Reviewed By: ryan

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D886