Fix bad link syntax Three-valued_logic

Author: andyw8

README.adoc

@@ -1062,7 +1062,7 @@ And you'll have to consider the fact that most non-trivial apps share a database
 === 3-state Boolean [[three-state-boolean]]
 
 With SQL databases, if a boolean column is not given a default value, it will have three possible values: `true`, `false` and `NULL`.
-Boolean operators [work in unexpected ways](https://en.wikipedia.org/wiki/Three-valued_logic) with `NULL`.
+Boolean operators https://en.wikipedia.org/wiki/Three-valued_logic[work in unexpected ways] with `NULL`.
 
 For example in SQL queries, `true AND NULL` is `NULL` (not false), `true AND NULL OR false` is `NULL` (not false). This can make SQL queries return unexpected results.