First, let's check php-curl has been installed on your server by
aptitude search php-curl
or aptitude search php5.6-curl
aptitude search php5.6-curl
if that hasn't been installed yet, let's install it by
sudo apt-get install php5.6-curl
I noticed extension=php_curl.dll was commented out in C:\wamp\bin\php\php5.4.12\php.ini but active via C:\wamp\bin\apache\Apache2.4.4\bin\php.ini.
extension=php_curl.dll
C:\wamp\bin\php\php5.4.12\php.ini
C:\wamp\bin\apache\Apache2.4.4\bin\php.ini
I found that uncommenting the line in C:\wamp\bin\php\php5.4.12\php.ini fixed my issue.