README: Fix Config Example

[amayer5125]

The oauth2 config is treated as a boolean. If someone copies and pastes this example they will get unexpected behavior because 'false' evaluates to true if converted to a boolean.

php > $oauth = 'false';
php > var_dump(isset($oauth) ? $oauth : false);
string(5) "false"
php > var_dump((bool)$oauth);
bool(true)