Fix link to beanstalkd protocol specification
Fix link to beanstalkd protocol specification

Beanstalkd no longer maintains a markdown version of the protocol spec -
it was removed in kr/beanstalkd@a0470f2

ptrofimov/beanstalk_console,pentium10/beanstalk_console,ptrofimov/beanstalk_console,ptrofimov/beanstalk_console,pentium10/beanstalk_console,pentium10/beanstalk_console