Close tmpfile after writing (#685)

* Close tmpfile after writing

Windows will not allow for deletion of a file with an open handle, 
close tmpfile after writing to prevent unencrypted tmpfiles out-living
the execution

* Update cmd/sops/edit.go

Co-authored-by: Adrian Utrilla <adrianutrilla@gmail.com>

* defer edited file close

Co-authored-by: Adrian Utrilla <adrianutrilla@gmail.com>

cmd/sops/edit.go

@@ -132,6 +132,9 @@ func editTree(opts editOpts, tree *sops.Tree, dataKey []byte) ([]byte, error) {
 	if err != nil {
 		return nil, common.NewExitError(fmt.Sprintf("Could not write output file: %s", err), codes.CouldNotWriteOutputFile)
 	}
+
+	// Close temporary file, since Windows won't delete the file unless it's closed beforehand
+	defer tmpfile.Close()
 
 	// Compute file hash to detect if the file has been edited
 	origHash, err := hashFile(tmpfile.Name())