trace: Fixed a minor typo in an error message.

Signed-off-by: Allan Caffee <allan.caffee@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

trace.c

@@ -50,7 +50,7 @@ static int get_trace_fd(int *need_close)
 		return fd;
 	}
 
-	fprintf(stderr, "What does '%s' for GIT_TRACE means ?\n", trace);
+	fprintf(stderr, "What does '%s' for GIT_TRACE mean?\n", trace);
 	fprintf(stderr, "If you want to trace into a file, "
 		"then please set GIT_TRACE to an absolute pathname "
 		"(starting with /).\n");