2011/lex: fix slide

Fixes golang/go#15851

Change-Id: If15adad47feb7d50632a7779004c6ff7a6a676d3
Reviewed-on: https://go-review.googlesource.com/23465
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/2011/lex.slide b/2011/lex.slide
index 04c04bd..d2fed7b 100644
--- a/2011/lex.slide
+++ b/2011/lex.slide
@@ -311,7 +311,7 @@
 
 Traditional lexer API: return next item.
 Includes the modified state machine runner.
-.
+
 .code lex/r59-lex.go /nextItem.returns/,/^}/
 
 * That's it