Fix typo in Chapter 2

codeaditya · marijnh · commit c6574ef0b67f · 2014-08-15T21:02:15.000+02:00
diff --git a/02_program_structure.txt b/02_program_structure.txt
@@ -891,7 +891,7 @@ headache.
 #######
 ----
 
-It may be useful to know that you can find the lengt of a string by
+It may be useful to know that you can find the length of a string by
 writing `.length` after it.
 
 [source,javascript]
