Change submodule urls (git -> https)

To work around too strict firewalls that block git's smart protocol port
9418.

Originally submitted at:

  https://github.com/wincent/Command-T/pull/103

Signed-off-by: Aleksandrs Ļedovskis <aleksandrs@ledovskis.lv>
Signed-off-by: Greg Hurrell <greg@hurrell.net>
doc: Add Aleksandrs Ļedovskis to AUTHORS section
Merge branch 'gh/aledovsky/https-gitmodules' into next

Originally submitted as:

  https://github.com/wincent/Command-T/pull/103

As I noted in my comments on the PR, there are a few things to bear in
mind about these submodule URLs:

- if some people can't access port 9418, there are others whose Git
  wasn't built with support for HTTPS, so there is no one default which
  will work for everyone
- HTTPS is considered a "dumb" transport among the protocols used by Git
- these submodules are development dependencies only, and not necessary
  for the functioning of the plug-in
- you can easily override entries in .gitmodules for your environment
  (eg. with git config submodule.vendor/vimball.url
  https://github.com/tomtom/vimball.rb.git or similar`)

Among those, the first reason is the real kicker, which is why I
previously closed a similar pull request (#54). I would do the same for
this one, although the fact that the protocols are currently mixed and
nobody has complained suggests that perhaps nobody is relying on git
transport, so what the hey...

* gh/aledovsky/https-gitmodules:
  doc: Add Aleksandrs Ļedovskis to AUTHORS section
  Change submodule urls (git -> https)