Fix incorrect chapter headers

fixes #11645

diff --git a/doc/19-library-reference.md b/doc/19-library-reference.md
index 503de7b98fa925a5cc8d5987acab45b47d44b7e2..8fffb8288003648c00afafd07439a3065888fecd 100644 (file)
--- a/doc/19-library-reference.md
+++ b/doc/19-library-reference.md
@@ -530,7 +530,7 @@ Returns a copy of the object. Note that for object elements which are
 reference values (e.g. objects such as arrays or dictionaries) the entire
 object is recursively copied.
 
-## <a id="object-to-string"></a> Object#to_string
+### <a id="object-to-string"></a> Object#to_string
 
 Signature:
 
@@ -544,7 +544,7 @@ Example:
 
     [ 3, true ].to_string() /* Returns "[ 3.000000, true ]" */
 
-## <a id="object-type-field"></a> Object#type
+### <a id="object-type-field"></a> Object#type
 
 Signature: