Upgrade joda-time to 2.8

2.8 is not the latest (2.8.1) but this is the version used by
Elasticsearch.

Change-Id: If5b488387b1c58d0e3e374dfa6846457d7519475

lib/joda/BUCK

diff --git a/lib/joda/BUCK b/lib/joda/BUCK
index 2401870..420a8ac 100644
--- a/lib/joda/BUCK
+++ b/lib/joda/BUCK
@@ -7,8 +7,8 @@
 
 maven_jar(
   name = 'joda-time',
-  id = 'joda-time:joda-time:2.7',
-  sha1 = '5599707a3eaad13e889f691b3af78c8c03842195',
+  id = 'joda-time:joda-time:2.8',
+  sha1 = '9f2785d7184b97d005a44241ccaf980f43b9ccdb',
   deps = [':joda-convert'],
   license = 'Apache2.0',
   exclude = EXCLUDE,