'EnvVersion' is short for 'envelope version' and isn't really related to the heka release version at all. The current value of 0.8 is maybe not the best choice (it's left over from the numbering started when we were still "metlog") but we shouldn't be changing it unless we're changing the actual structure of our message objects.

This opens up a bigger issue re: how to manage compatibility through protocol and data model changes, which we should probably think through a bit more carefully than we have.