That's all up to you. I'd bump it in any way whenever you expand or alter the library. You can consider to split the version in a "major version" and a "minor version". E.g. 1.0, 1.1, 1.2, 2.0, 2.1, etc to distinguish between major and minor changes. E.g. just bump the minor version when you add new attributes and bump the major version when you add brand new tags and/or change the behaviour of existing tags.
At least, as long as every change is documented per version, the endusers don't really care about how the version numbers develops. It has only more potential benefits for the marketing.