fix minor error in covertGDP documentation

R/convertGDP.R

@@ -76,7 +76,7 @@
 #'     \item "regional_average": missing conversion factors in the source object are replaced with
 #'     the regional average of the region to which the country belongs. This requires a region-mapping to
 #'     be passed to the function, see the with_regions argument.
-#'     \item "with USA": missing conversion factors in the source object are replaced with
+#'     \item "with_USA": missing conversion factors in the source object are replaced with
 #'     the conversion factors of the USA.
 #'   }
 #'   Can also be a vector with "linear" as first element, e.g. c("linear", 0) or c("linear", "no_conversion"),