github_repository documentation incorrect argument for delete_branch_on_merge

[deppy]

The documentation provides an argument called auto_delete_head_branch but the code calls it delete_branch_on_merge.

You can verify that auto_delete_head_branch is incorrect with:

resource "github_repository" "example" {
  name                                   = "example"
  description                         = "My awesome codebase"
  delete_branch_on_merge = true
}

and then simply run terraform validate

[anGie44]

hi @deppy! Just wanted to follow-up and note I'm going to close this as a recent merge of #408 addresses what you've pointed out. Thanks for the work you put into creating the issue/PR though :)