[spotbugs] Silence warning about unwritten field written by gson

It seems spotbugs does not recognize that this data is written by gson.

Change-Id: I0704d489971c0ab6ec398083f211c409061e7661
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.lfs.server/findBugs/FindBugsExcludeFilter.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<FindBugsFilter>
+<!-- Field is written by gson, seems like spotbugs doesn't recognize this -->
+     <Match>
+       <Class name="org.eclipse.jgit.lfs.server.LfsObject" />
+       <Bug pattern="UWF_UNWRITTEN_FIELD" />
+     </Match>
+</FindBugsFilter>