Update index.js

google spreadsheet removes underscores in field name.
this changes follows google spreadsheed naming behaviour and lets us update spreadsheet fields such as _id by specifying _id in the fieldname.
Merge pull request #11 from Somsy/patch-1

Update index.js
Merge pull request #10 from k88hudson/master

Check if worksheet_id is a number and greater than 0
Revert "Check if worksheet_id is a number and greater than 0, since 0 is a valid worksheet id"

This reverts commit 2b53c69fa7738de3f5f1caa1662b3172df5514b4.