Fix typo in geom_density() description (#2508)

Author: pkq

R/geom-density.r

@@ -1,7 +1,7 @@
 #' Smoothed density estimates
 #'
 #' Computes and draws kernel density estimate, which is a smoothed version of
-#' the histogram. This is a useful alternative to the histogram if for continuous
+#' the histogram. This is a useful alternative to the histogram for continuous
 #' data that comes from an underlying smooth distribution.
 #'
 #' @eval rd_aesthetics("geom", "density")