运行gulp的时候总会扔出这个错误
[18:49:20] Requiring external module babel-register
assert.js:350
throw err;
^

AssertionError [ERR_ASSERTION]: Task function must be specified
at Gulp.set [as _setTask] (/Users/jinailan/es6/node_modules/undertaker/lib/set-task.js:10:3)
at Gulp.task (/Users/jinailan/es6/node_modules/undertaker/lib/task.js:13:8)
at Object. (/Users/jinailan/es6/tasks/default.js:3:6)
at Module._compile (internal/modules/cjs/loader.js:689:30)
at loader (/Users/jinailan/es6/node_modules/babel-register/lib/node.js:144:5)
at Object.require.extensions.(anonymous function) [as .js] (/Users/jinailan/es6/node_modules/babel-register/lib/node.js:154:7)
at Module.load (internal/modules/cjs/loader.js:599:32)
at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
at Function.Module._load (internal/modules/cjs/loader.js:530:3)
at Module.require (internal/modules/cjs/loader.js:637:17)
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