Fix root element namespace

cf. #21

test/data/articles/zb_preview.xml

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="UTF-8"?><oai_zbmath_preview xmlns:zbmath="https://zbmath.org/zbmath/elements/1.0/" xmlns:oai_zbmath_preview="https://zbmath.org/OAI/2.0/oai_zbmath_preview/">
+<?xml version="1.0" encoding="UTF-8"?><oai_zb_preview:zbmath xmlns:zbmath="https://zbmath.org/zbmath/elements/1.0/" xmlns:oai_zb_preview="https://zbmath.org/OAI/2.0/oai_zbmath_preview/">
     <zbmath:author>Maynard, James</zbmath:author>
     <zbmath:author_ids>
         <zbmath:author_id>maynard.james</zbmath:author_id>
@@ -143,4 +143,4 @@
         we replaced the data with the string 'zbMATH Open Web Interface contents
         unavailable due to conflicting licenses.'
     </zbmath:rights>
-</oai_zbmath_preview>
+</oai_zb_preview:zbmath>

xslt/articles/xslt-article-transformation.xslt

@@ -1,15 +1,15 @@
 <?xml version="1.0" encoding="ISO-8859-1"?>
 <xsl:stylesheet version="1.0"
                 xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
-                xmlns:oai_zbmath_preview="https://zbmath.org/OAI/2.0/oai_zbmath_preview/"
+                xmlns:oai_zb_preview="https://zbmath.org/OAI/2.0/oai_zbmath_preview/"
                 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xmlns:zbmath="https://zbmath.org/zbmath/elements/1.0/"
                 exclude-result-prefixes="xsi oai_zb_preview">
 
 
 <xsl:output method="xml" indent="yes"/>
 <xsl:template match="/">
-  <oai_zbmath_preview>
+  <oai_zb_preview:zbmath>
     <zbmath:author>
       <xsl:value-of select="root/result/contributors/authors/name"/>
     </zbmath:author>
@@ -162,6 +162,6 @@
         we replaced the data with the string 'zbMATH Open Web Interface contents
         unavailable due to conflicting licenses.'
     </zbmath:rights>
-  </oai_zbmath_preview>
+  </oai_zb_preview:zbmath>
 </xsl:template>
 </xsl:stylesheet>