correcting the number of output formats

Author: gregsdennis

jsonschema-core.xml

@@ -2715,7 +2715,7 @@
 
             <section title="Output Formats">
                 <t>
-                    This specification defines four output formats.  See the "Output Structure"
+                    This specification defines three output formats.  See the "Output Structure"
                     section for the requirements of each format.
                     <list>
                         <t>