Downgrade TEI stylesheets to 6.17

for compatibility with Isaballa's stylesheet

git-svn-id: https://develop.sub.uni-goettingen.de/repos/textgrid/trunk/services/aggregator@13874 7c539038-3410-0410-b1ec-0f2a7bf1c452

pom.xml

@@ -32,7 +32,7 @@
       <guava-version>13.0.1</guava-version>
       <junit-version>4.10</junit-version>
       <spring-version>3.2.2.RELEASE</spring-version>
-      <tei-xsl-version>6.28</tei-xsl-version>
+      <tei-xsl-version>6.17</tei-xsl-version>
    </properties>
 
 	  <repositories>