Add missing period

src/epub/text/endnotes.xhtml

@@ -16,7 +16,7 @@
 					<p>In the story, as it appeared in serial form, the name of the poison occurred. It has been represented to the author (and he agrees) that it is wholly undesirable that the name of this drug should appear in a work of fiction. It is one well known to oculists and its action is faithfully described in these pages. <a href="chapter-1.xhtml#noteref-2" epub:type="backlink">↩</a></p>
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-					<p>Busy: a busy fellow, detective <a href="chapter-3.xhtml#noteref-3" epub:type="backlink">↩</a></p>
+					<p>Busy: a busy fellow, detective. <a href="chapter-3.xhtml#noteref-3" epub:type="backlink">↩</a></p>
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