Increase margin top of figure caption from 2 to 4mm

Change-Id: I5d5ff69756b1e8b19ab2499efd7390b51971f5de
diff --git a/inst/rmarkdown/templates/posterdown_ids/resources/template.html b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
index f4013d1..fcf2e74 100644
--- a/inst/rmarkdown/templates/posterdown_ids/resources/template.html
+++ b/inst/rmarkdown/templates/posterdown_ids/resources/template.html
@@ -365,6 +365,9 @@
 line-height: 1;
 border-radius: 2mm;
 }
+.figure > .caption {
+margin-top: 4mm;
+}
 .caption {
 font-size: 20pt;
 margin-left: auto;