Update doc tool dependency pinning.
Update doc tool dependency pinning.

Updates the doc tool temporarily to fix the unexpected inclusion of
`Input` or validated shapes in package list root on
http://docs.aws.amazon.com/sdk-for-go/api/.

Fix #658

calgaryscientific/aws-sdk-go,myshen/aws-sdk-go,myshen/aws-sdk-go,calgaryscientific/aws-sdk-go,jjeffery/aws-sdk-go,agworld/aws-sdk-go,yxd-hde/aws-sdk-go,agworld/aws-sdk-go,myshen/aws-sdk-go,radeksimko/aws-sdk-go,yxd-hde/aws-sdk-go,calgaryscientific/aws-sdk-go,jasdel/aws-sdk-go,yxd-hde/aws-sdk-go,radeksimko/aws-sdk-go,zmarois/aws-sdk-go,aws/aws-sdk-go,xibz/aws-sdk-go,jjeffery/aws-sdk-go,agworld/aws-sdk-go,xibz/aws-sdk-go,zmarois/aws-sdk-go,zmarois/aws-sdk-go,zmarois/aws-sdk-go,radeksimko/aws-sdk-go,jjeffery/aws-sdk-go,myshen/aws-sdk-go,calgaryscientific/aws-sdk-go,xibz/aws-sdk-go,xibz/aws-sdk-go,radeksimko/aws-sdk-go,agworld/aws-sdk-go,yxd-hde/aws-sdk-go