Update l3build.dtx

l3build.dtx

@@ -369,7 +369,7 @@
 % As well as these targets, the system recognises the options
 % \begin{itemize}
 % \item |--config| (|-c|) Configuration(s) to use for testing
-% \item |--date| Date to use when tagging data
+% \item |--date| (|-d|) Date to use when tagging data
 % \item |--debug| Runs the target in debug mode (not supported by all targets)
 % \item |--dirty| Skips cleaning up of the test area
 % \item |--dry-run| Runs the \texttt{install} target but does not copy