Facebook share dialog uses "caption" instead of "description"

[dm-coding]

I found that I was dissatisfied with the way the Facebook sharer uses the selected text to populate the caption element of the sharer dialog box instead of the larger, bolder description element. I have modified the code as below and would be grateful for your feedback.

dm-coding/selection-sharer@55e8ad6...djcf:56a33d63dbe01887cbd8b2209ef856ec0bdd9558

The most relevant lines are 243 and 245.