Rename NoZeroBeforeDecimal -> LeadingZero

This name was longer than it needed to be. `LeadingZero` captures the
essence of the lint much better, and with fewer characters to boot.

Change-Id: I2b24ee48f082ddfe3c42fe7ff4215c09636f3203
Reviewed-on: https://gerrit.causes.com/29751
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>