/usr/bin/env perl

I like to use the 'env' command, as it's more and more
common for people (thanks to perlbrew) to use a 'perl' which is not
/usr/bin/perl
Always put your seatbelt on. :-)
Pod::Usage for --help and --man

Plus, helps get the POD going
Bringing variable definition and use closer

... and remove eval {} or die "", as in this
case the original die messages would have as much
information as what the custom die had.

Path::Tiny
use IO::Prompt::Simple

Maybe overkill in this case, but oh-so-nice. :-)
As Michael Jackson and McCarthy once sung...

Say, say, say..
use YAML instead of JSON

it's a question of taste, but typically YAML is a tad
easier on the eyes and fingers of humans.
divide functionality in functions
and then we up our game to MooseX::App

so now we can do

    gdrivebackup.pl --help

    gdrivebackup.pl init

    gdrivebackup.pl backup --source-file XXX --target_doc YYY --file_type text/plain
Merge pull request #1 from yanick/notes-and-stuff

Notes and stuff