pin typescript to the version whose API we support
pin typescript to the version whose API we support

Fixes issue #200.

hess-g/tsickle,drjanitor/tsickle,lucidsoftware/tsickle,hess-g/tsickle,ncfxy/tsickle,lucidsoftware/tsickle,alexeagle/tsickle,angular/tsickle,drjanitor/tsickle,angular/tsickle,lucidsoftware/tsickle,drjanitor/tsickle,drjanitor/tsickle,alexeagle/tsickle,ncfxy/tsickle,alexeagle/tsickle,ncfxy/tsickle