Don’t upgrade to future versions unnecessarily

Closes #55

commit 4914c5bbf401711b61d9a54330532175a51a167c
Author: Rhys Arkins <rhys@keylocation.sg>
Date:   Tue Jan 17 12:45:45 2017 +0100

    Update debug

commit 55c8307381397399afda01038b6c50416cba27a3
Author: Rhys Arkins <rhys@keylocation.sg>
Date:   Tue Jan 17 12:44:08 2017 +0100

    Ignore versions newer than “latest”

commit 8aa3e7daa937c0d86f89e1d704853ebee46a54a8
Author: Rhys Arkins <rhys@keylocation.sg>
Date:   Tue Jan 17 11:17:31 2017 +0100

    Ignore futures if current is not future