Update dependency for PlotlyBase 0.8.15

needed for `add_layout_image!

Author: sglyon

Project.toml

@@ -22,7 +22,7 @@ WebIO = "0f1e0344-ec1d-5b48-a673-e5cf874b6c29"
 Blink = "0.12"
 JSExpr = "0.5, 1"
 JSON = "0.20, 0.21"
-PlotlyBase = "0.8.9"
+PlotlyBase = "0.8.15"
 Reexport = "0.2, 1"
 Requires = "1.0"
 WebIO = "0.8"