Add possibility to change branch name

[damda58]

Add possibility to change branch name

for example 'main' instead of 'master'

[mattvw]

Missed changing a reference to master branch on line 85 (original script) in the pull_initialize function (and the comment above the line). Just FYI.

[stevejenkins]

Since it's now GitHub's default behavior to set up a "main" instead of "master" branch, I will work on migrating this project's current "master" branch to "main" as well as update the code to do the same for the users' private repos.