From the announcement:
Today we are releasing Hammer Wars v1.5, a fresh take on our newest game.
After the release of Hammer Wars v1.0 we went back and played it some more, and felt that the game was good… but could be better. One of our main goals with the game was to make it be a small and fast game, but some of its mechanics hindered that.
This release changes the way that activations work, which makes the game considerably faster and clearer. There are also some other changes to units and goals, but they are fairly minor and you might not even notice.
So yea, its not changed enough to be v2.0, its changed way more than just v1.1… so this is v1.5!