Fix checkstyle xml header

Move xml version to the top of the file to avoid illformed xml file.

https://jira.apache.org/jira/projects/CRAIL/issues/CRAIL-53

Signed-off-by: Jonas Pfefferle <pepperjo@apache.org>

checkstyle.xml

@@ -1,3 +1,4 @@
+<?xml version="1.0"?>
 <!--
   ~
   ~ Licensed to the Apache Software Foundation (ASF) under one or more
@@ -15,7 +16,6 @@
   ~ See the License for the specific language governing permissions and
   ~ limitations under the License.
   -->
-<?xml version="1.0"?>
 <!DOCTYPE module PUBLIC
           "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
           "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">