#3261: Update 'base.dockerfile' with updated git

[jeff1evesque]

Resolves #3261.

[jeff1evesque]

We've verified that our adjusted changes are acceptable:

root@vagrant-ubuntu-trusty-64:/vagrant# apt-get -y install git=1:1.9.1*
Reading package lists... Done
Building dependency tree
Reading state information... Done
git is already the newest version.
Selected version '1:1.9.1-1ubuntu0.7' (Ubuntu:14.04/trusty-updates [amd64]) for 'git'
0 upgraded, 0 newly installed, 0 to remove and 9 not upgraded.

[coveralls]

Coverage remained the same at 29.15% when pulling add7297 on bug-3261 into 6589622 on master.