change referer 'CURLOPT_REFERER'

[atomGit]

/modules/checkers/http.php
line 194, 195:

//Add a semi-plausible referer header to avoid tripping up some bot traps
curl_setopt($ch, CURLOPT_REFERER, home_url());

i'd like to change the referer to google to see if i can avoid some '403 Forbidden' results (vimeo.com) - how do i do this - is the following correct:
curl_setopt($ch, CURLOPT_REFERER, 'google.com');

or do i need to keep the brackets:
curl_setopt($ch, CURLOPT_REFERER, 'google.com'());