composer安装版本问题

Problem 1
   - Installation request for doctrine/dbal v2.6.1 -> satisfiable by doctrine/dbal[v2.6.1].
   - doctrine/dbal v2.6.1 requires php ^7.1 -> your PHP version (7.0.16) does not satisfy that requirement.
 Problem 2
   - doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (7.0.16) does not satisfy that requirement.
   - doctrine/instantiator 1.1.0 requires php ^7.1 -> your PHP version (7.0.16) does not satisfy that requirement.
   - Installation request for doctrine/instantiator 1.1.0 -> satisfiable by doctrine/instantiator[1.1.0].