Fix typo

Author: handrews

jsonschema-core.xml

@@ -1386,7 +1386,7 @@
                     </t>
                     <t>
                         The "$anchor" and "$dynamicAnchor" keywords are used to specify such
-                        a fragments.  They are identifier keywords that can only be used to create
+                        fragments.  They are identifier keywords that can only be used to create
                         plain name fragments, rather than absolute URIs as seen with "$id".
                         The behavior of the created fragment is identical for both keywords.
                     </t>