Update lexical_cast in documentation build.

doc/Jamfile.v2

@@ -41,7 +41,7 @@ boostbook doc
     <dependency>../libs/accumulators/doc//opdoc.xml
     <dependency>../libs/accumulators/doc//accumulators
     <dependency>../libs/circular_buffer/doc//standalone/<format>docbook
-    <dependency>../libs/conversion/doc//lexical_cast
+    <dependency>../libs/lexical_cast/doc//lexical_cast
     <dependency>../libs/core/doc//core
     <dependency>../libs/core/doc//ref_reference
     <dependency>../libs/chrono/doc//chrono
@@ -94,7 +94,7 @@ boostbook doc
 
     <implicit-dependency>../libs/accumulators/doc//accumulators
     <implicit-dependency>../libs/chrono/doc//chrono
-    <implicit-dependency>../libs/conversion/doc//lexical_cast
+    <implicit-dependency>../libs/lexical_cast/doc//lexical_cast
     <implicit-dependency>../libs/core/doc//core
     <implicit-dependency>../libs/functional/hash/doc//hash
     #<implicit-dependency>../libs/type_traits/doc//type_traits