Update section number of F&O reference

Author: afs

spec/index.html

@@ -7601,7 +7601,7 @@ <h3>XPath Constructor Functions</h3>
           [[[XPATH-FUNCTIONS-31]]] [[XPATH-FUNCTIONS-31]] in
           section 
           <a data-cite="XPATH-FUNCTIONS-31#casting-from-primitive-to-primitive"
-          >17.1 Casting from primitive types to primitive types</a>.
+          >19.1 Casting from primitive types to primitive types</a>.
           SPARQL constructors include all of the XPath constructors for
           the <a href="#operandDataTypes">SPARQL operand datatypes</a> plus
           the <a href="#operandDataTypes">additional datatypes</a> imposed by