Counting commits since a tag takes into account only first parents

[rtimush]

The commit counting method is different from what git describe uses — it counts commits on the path via the first parents only. This is a bit arbitrary, and also can cause ordering issues when a merge commit version precedes a version of the parent because it happened to be the second one. Is it intentional?

*  - 1.0.1-2-...
|\
| *  - 1.0.1-3-...
* |  - 1.0.1-1-...
| *  - 1.0.1-2-...
| |
| *  - 1.0.1-1-...
|/
*  - 1.0.0

And thank you for the plugin!