I failed to note you are using endnote online rather than the desktop program. You will need to request that Clarivate correct the output style they provide for Endnote online.
You can give the info here, http://endnote.com/downloads/output-style-request but I would probably be inventive using the fields to indicate you need it updated for the online version and that you simply need the colon bolded after the volume number. – perhaps in the journal title?
I have no idea how long a request like this takes. You might want to address it more directly with Tech Support.