[keyserver] Consistency for keyserver/bash folder

Summary:

1. chmod 755 source-nvm.sh (other files have executable bit set)
2. git mv backup_phabricator.sh backup-phabricator.sh (other files use dashes instead of underscores)

Test Plan:

1. I updated the prod cronjob for backing up Phabricator (which isn't running right now anyways, currently relying on AWS RDS)
2. I git grep'd for backup_phabricator and found nothing
3. I'm fairly confident chmod 755 will have no ill effects

Reviewers: atul, varun

Reviewed By: varun

Subscribers: palys-swm, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3898