JATS writer: wrap figure caption in <p> to fix validation (#5292)

closes #5290

src/Text/Pandoc/Writers/JATS.hs

@@ -230,7 +230,7 @@ blockToJATS opts (Para [Image (ident,_,kvs) txt
   let (maintype, subtype) = imageMimeType src kvs
   let capt = if null txt
                 then empty
-                else inTagsSimple "caption" alt
+                else inTagsSimple "caption" $ inTagsSimple "p" alt
   let attr = [("id", ident) | not (null ident)] ++
              [(k,v) | (k,v) <- kvs, k `elem` ["fig-type", "orientation",
                                               "position", "specific-use"]]

test/writer.jats

@@ -835,7 +835,7 @@ These should not be escaped:  \$ \\ \&gt; \[ \{</preformat>
   <title>Images</title>
   <p>From “Voyage dans la Lune” by Georges Melies (1902):</p>
   <fig>
-    <caption>lalune</caption>
+    <caption><p>lalune</p></caption>
     <graphic mimetype="image" mime-subtype="jpeg" xlink:href="lalune.jpg" xlink:title="Voyage dans la Lune" />
   </fig>
   <p>Here is a movie