Fix order of diamond color factor. (#3146)

* Update diamonds docs

Put the order that the levels of `diamonds$color` are mentioned in the docs match their order in the variable.

See #3146 (comment)

Author: jrnold

R/data.R

@@ -8,7 +8,7 @@
 #'   \item{price}{price in US dollars (\$326--\$18,823)}
 #'   \item{carat}{weight of the diamond (0.2--5.01)}
 #'   \item{cut}{quality of the cut (Fair, Good, Very Good, Premium, Ideal)}
-#'   \item{color}{diamond colour, from J (worst) to D (best)}
+#'   \item{color}{diamond colour, from D (best) to J (worst)}
 #'   \item{clarity}{a measurement of how clear the diamond is (I1 (worst), SI2,
 #'     SI1, VS2, VS1, VVS2, VVS1, IF (best))}
 #'   \item{x}{length in mm (0--10.74)}