Add missing namespace and XSD to SpotBugs filter file.
diff --git a/findbugs-exclude-filter.xml b/findbugs-exclude-filter.xml
index c4d319f..015438a 100644
--- a/findbugs-exclude-filter.xml
+++ b/findbugs-exclude-filter.xml
@@ -21,6 +21,9 @@
   false positive nature has been analyzed individually and they have been
   put here to instruct findbugs it must ignore them.
 -->
-<FindBugsFilter>
+<FindBugsFilter
+    xmlns="https://github.com/spotbugs/filter/3.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="https://github.com/spotbugs/filter/3.0.0 https://raw.githubusercontent.com/spotbugs/spotbugs/3.1.0/spotbugs/etc/findbugsfilter.xsd">
 
 </FindBugsFilter>