Convert single quotes to double quotes

src/epub/text/chapter-2-6.xhtml

@@ -27,7 +27,7 @@
 			<p>Heidi immediately read to her two listeners, as follows:⁠—</p>
 			<blockquote epub:type="z3998:letter">
 				<p epub:type="z3998:salutation">Dear <span epub:type="z3998:recipient">Heidi</span>:⁠—</p>
-				<p>We are all packed up and shall travel in two or three days. Papa is leaving, too, but not with us, for he has to go to Paris first. The dear doctor visits us now every day, and as soon as he opens the door, he calls, ‘Away to the Alp!’ for he can hardly wait for us to go. If you only knew how he enjoyed being with you last fall! He came nearly every day this winter to tell us all about you and the grandfather and the mountains and the flowers he saw. He said that it was so quiet in the pure, delicious air, away from towns and streets, that everybody has to get well there. He is much better himself since his visit, and seems younger and happier. Oh, how I look forward to it all! The doctor’s advice is, that I shall go to Ragatz first for about six weeks, then I can go to live in the village, and from there I shall come to see you every fine day. Grandmama, who is coming with me, is looking forward to the trip too. But just think, Miss Rottenmeier does not want to go. When grandmama urges her, she always declines politely. I think Sebastian must have given her such a terrible description of the high rocks and fearful abysses, that she is afraid. I think he told her that it was not safe for anybody, and that only goats could climb such dreadful heights. She used to be so eager to go to Switzerland, but now neither Tinette nor she wants to take the risk. I can hardly wait to see you again!</p>
+				<p>We are all packed up and shall travel in two or three days. Papa is leaving, too, but not with us, for he has to go to Paris first. The dear doctor visits us now every day, and as soon as he opens the door, he calls, “Away to the Alp!” for he can hardly wait for us to go. If you only knew how he enjoyed being with you last fall! He came nearly every day this winter to tell us all about you and the grandfather and the mountains and the flowers he saw. He said that it was so quiet in the pure, delicious air, away from towns and streets, that everybody has to get well there. He is much better himself since his visit, and seems younger and happier. Oh, how I look forward to it all! The doctor’s advice is, that I shall go to Ragatz first for about six weeks, then I can go to live in the village, and from there I shall come to see you every fine day. Grandmama, who is coming with me, is looking forward to the trip too. But just think, Miss Rottenmeier does not want to go. When grandmama urges her, she always declines politely. I think Sebastian must have given her such a terrible description of the high rocks and fearful abysses, that she is afraid. I think he told her that it was not safe for anybody, and that only goats could climb such dreadful heights. She used to be so eager to go to Switzerland, but now neither Tinette nor she wants to take the risk. I can hardly wait to see you again!</p>
 				<p>Goodbye, dear Heidi, with much love from grandmama,</p>
 				<footer>
 					<p epub:type="z3998:valediction">I am your true friend,</p>