1.5.1

In 1.5.0, I added a new way of bumping the build number, by using a time stamp instead of an incremental step. However, the first time I use this, it sets the "library version" flag, for which this format is invalid. This happened in 1.5.0, which meant that it could not be installed with Carthage, nor built in Xcode. This version fixes this error.