Fix typo in glossary
Reported privately by Justin Pryzby
Contains the values of <glossterm linkend="glossary-tuple">row</glossterm>
attributes (i.e. the data) for a
<glossterm linkend="glossary-relation">relation</glossterm>.
- The heap is realized within one of more
+ The heap is realized within one or more
<glossterm linkend="glossary-file-segment">file segments</glossterm>
in the relation's <glossterm linkend="glossary-fork">main fork</glossterm>.
</para>
