Upgrade joda-time to version 2.8

To match the version used in Gerrit.

Change-Id: I3494f00bafeda327428a60d5492748b398feedb8

lib/BUCK

diff --git a/lib/BUCK b/lib/BUCK
index db57044..a3cb2e6 100644
--- a/lib/BUCK
+++ b/lib/BUCK
@@ -18,8 +18,8 @@
 
 maven_jar(
   name = 'joda-time',
-  id = 'joda-time:joda-time:2.3',
-  sha1 = '56498efd17752898cfcc3868c1b6211a07b12b8f',
+  id = 'joda-time:joda-time:2.8',
+  sha1 = '9f2785d7184b97d005a44241ccaf980f43b9ccdb',
   exclude = [
     'META-INF/LICENSE.txt',
     'META-INF/NOTICE.txt',