"The gatsby-source-google-sheets plugin has generated no Gatsby nodes" when sheet has a single row

[j-nolan]

Steps to reproduce:

1. Query a spreadsheet that only has a single row
2. gatsby develop

   success open and validate gatsby-config — 0.007 s
   ...
   ⠁ FETCHING SHEET function fetchData(_x2, _x3, _x4) {
   return _ref.apply(this, arguments);
   }
   warning The gatsby-source-google-sheets plugin has generated no Gatsby nodes. Do you need it?
   success source and transform nodes — 1.032 s
   ...

And indeed, graphiql shows me that no node are created. It works fine with sheets that contain at least two rows.

[j-nolan]

Update: this is because the first row is considered the header. I was mistaken about how the spreadsheet should be formatted.

Request is that documentation should be updated to make it clear that the first row is the header.

Happy to make a PR if maintainers agree.

[drewatk]

Closing in favor of #22