Fix chapter number

src/ch06-02-match.md

@@ -6,7 +6,7 @@ Rust has an extremely powerful control flow construct called `match` that
 allows you to compare a value against a series of patterns and then execute
 code based on which pattern matches. Patterns can be made up of literal values,
 variable names, wildcards, and many other things; [Chapter
-18][ch19-00-patterns]<!-- ignore --> covers all the different kinds of patterns
+19][ch19-00-patterns]<!-- ignore --> covers all the different kinds of patterns
 and what they do. The power of `match` comes from the expressiveness of the
 patterns and the fact that the compiler confirms that all possible cases are
 handled.