Updated GoogleDoc class to work with new(er) spreadsheets

I noticed the `gid` parameter is ignored when fetching the example spreadsheet included with the app template. However, the `gid` parameter does work when fetching newer spreadsheets.

So, I changed the `GoogleDoc` class to omit the `gid` param so that all sheets in a spreadsheet will be downloaded by default. Also changed the `fab text.update` command to accept a `gid` argument in case you only want to fetch a specific sheet from your spreadsheet.