Update ecma262 section numbers

Author: Relequestual

jsonschema-core.xml

@@ -545,7 +545,7 @@
                     Keywords MAY use regular expressions to express constraints, or constrain
                     the instance value to be a regular expression.
                     These regular expressions SHOULD be valid according to the regular expression
-                    dialect described in <xref target="ecma262">ECMA 262, section 15.10.1</xref>.
+                    dialect described in <xref target="ecma262">ECMA 262, section 21.2.1</xref>.
                 </t>
                 <t>
                     Furthermore, given the high disparity in regular expression constructs support,