Fix incorrect field name for user_login
Fix incorrect field name for user_login

Updated to the correct variable name so that user input is saved correctly. Resolve #55
sassafrastech/wordpress-social-login,hubdotcom/wordpress-social-login,ftena/wordpress-social-login,NickIvanter/wordpress-social-login,hubdotcom/wordpress-social-login,NickIvanter/wordpress-social-login,sassafrastech/wordpress-social-login,miled/wordpress-social-login,miled/wordpress-social-login,miled/wordpress-social-login,miled/wordpress-social-login,hubdotcom/wordpress-social-login,sassafrastech/wordpress-social-login,ftena/wordpress-social-login,hubdotcom/wordpress-social-login,NickIvanter/wordpress-social-login,NickIvanter/wordpress-social-login,ftena/wordpress-social-login,sassafrastech/wordpress-social-login,ftena/wordpress-social-login