#169 Fixed repeated updates for the unchanged target

[oleksandr-danylchenko]

Issue - #169

such events as "releasing the Shift" or "releasing the handlebar" are considered as "selection finishing events". In both cases, the upsertCurrentTarget gets called almost immediately. However, a user can simply press Shift or tap over the handlebar, which will also lead to redundant updateTarget calls upon the initial creation.

The reason for such behavior was a missing check of whether the target that's about to be updated is different from the existing one.

Changes Made

I added the updated property comparison between the existing annotation target and the currentTarget. That effectively filters out repeated Shift key releases or taps over the handlebar, because there's no selectionchange event emitter that solely leads the updated prop change.

[rsimon]

Thanks for this!!