Configure base to a branch other than master

[siddharthkp]

from @Haroenv: thing which would make it a lot nicer too is if the comparison would be to the base branch on GitHub (instead of always master), since that way you get a pure diff

[Haroenv]

relevant code I think is:

bundlesize/src/reporter.js

Line 19 in 00c7d22

if (currentEvent === 'push' && currentBranch === 'master') {

Here only the master size is persisted, but instead we need to either compute the size of the target branch, or save the state of every branch instead of only master.

Frontend it also requires some changes like changing master to target (or the name of the target)

bundlesize/store/views/build.pug

Line 22 in 00c7d22

<div class="light label master">MASTER</div>