Fix bot's 'Failed to create a repository: {"message":"Server Error"}' error message

When GHOrganization#publicize method argument is a GHUser that is already publicizing its membership, GitHub returns error 500, causing the API to fail.

This commit fixes this behaviour with a prior verification whether the organization has the user or not.

This verification is made with GHOrganization#hasPublicMembers(GHUser). As this method is not available in github-api-1.28, the pom.xml was updated to version 1.37, which contains the missing method.

I used TupiLabs organization and some of its repositories/members to test this error, and this change seems to fix it. 

Thanks