Bump Babel requirement to >=1.0

The Zuul client uses babel.dates.format_timedelta which was introduced
with 1.0 http://babel.pocoo.org/docs/changelog/#version-1-0

Ubuntu Precise has 0.9.6 causing the Zuul client to abort because of the
missing method.

Change-Id: I60ed0d61c97091c17a926770ed1a02f1156ec5e0
diff --git a/requirements.txt b/requirements.txt
index 92d8e7c..eabcef3 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -17,5 +17,5 @@
 python-swiftclient>=1.6
 python-keystoneclient>=0.4.2
 PrettyTable>=0.6,<0.8
-babel
+babel>=1.0
 six>=1.6.0