[Rd] trivial typo in system.Rd

[Ben Bolker]

Index: system.Rd
===================================================================
--- system.Rd	(revision 53611)
+++ system.Rd	(working copy)
@@ -181,7 +181,7 @@
     \item The most important difference is that on a Unix-alike
     \code{system} launches a shell which then runs \code{command}.  On
     Windows the command is run directly -- use \code{shell} for an
-    interface which runs \code{comamnd} \emph{via} a shell (by default
+    interface which runs \code{command} \emph{via} a shell (by default
     the Windows shell \command{cmd.exe}, which has many differences from
     the POSIX shell).