Update semantics

src/epub/text/colophon.xhtml

@@ -12,7 +12,7 @@
 				<img alt="The Standard Ebooks logo" src="../images/logo.svg" epub:type="z3998:publisher-logo se:image.color-depth.black-on-transparent"/>
 			</header>
 			<p><i epub:type="se:name.publication.book">Fables</i><br/>
-			was initially collected between 620 and 564 <abbr class="era">BCE</abbr> by<br/>
+			was initially collected between 620 and 564 <abbr epub:type="se:era">BCE</abbr> by<br/>
 			<a href="https://en.wikipedia.org/wiki/Aesop">Aesop</a>,<br/>
 			and further added to by many people over the following millennium.<br/>
 			It was translated from Greek in 1912 by<br/>