Fix unaligned args in api_docs/python/tf/contrib/learn/Evaluable (#10423)

This commit fixes unaligned args in api_docs/python/tf/contrib/learn/Evaluable
Signed-off-by: NYong Tang <yong.tang.github@outlook.com>

tensorflow/contrib/learn/python/learn/evaluable.py

@@ -90,7 +90,6 @@ class Evaluable(object):
         friendly names for the metric to a `MetricSpec` object defining which
         model outputs to evaluate against which labels with which metric
         function.
-
         Metric ops should support streaming, e.g., returning `update_op` and
         `value` tensors. For example, see the options defined in
         `../../../metrics/python/ops/metrics_ops.py`.