Fix duplicated phrase

Author: Relequestual

jsonschema-core.xml

@@ -549,7 +549,7 @@
                 </t>
                 <t>
                     Regular expressions SHOULD be built with the "u" flag (or equivilent) to provide
-                    Unicode support, or processed in such a way which provides which provides Unicode
+                    Unicode support, or processed in such a way which provides Unicode support,
                     as defined by ECMA 262.
                 </t>
                 <t>