Add chloropleth->choropleth

This is a fairly common typo for people encountering the word _choropleth_ for the first time, since in English the prefix _chloro-_ is familiar whereas `choro-` is relatively rare.

Author: nathanjmcdougall

codespell_lib/data/dictionary.txt

@@ -12659,6 +12659,7 @@ chked->checked
 chlid->child
 chlidren->children
 chlids->children
+chloropleth->choropleth
 chnage->change
 chnaged->changed
 chnages->changes