Merge branch 'topic/field_predicate_doc' into 'master'

Fix wrong example given in the 'field predicate' doc section

Closes #189

See merge request eng/libadalang/langkit-query-language!211

user_manual/source/language_reference.rst

@@ -890,7 +890,7 @@ construct in the introduction, and it's one of the simplest kind of patterns.
 
 .. code-block:: lkql
 
-   select ObjectDecl(p_default_val(): IntLiteral)
+   select ObjectDecl(f_default_expr : IntLiteral)
 
 Property Call Predicate
 """""""""""""""""""""""