message: Minor error message fix in TPUEstimator.
diff: @@ -2641,7 +2641,7 @@ class _CapturedObject(object):
  def capture(self, o):
  if self._captured:
  raise RuntimeError(
  - 'InternalError: Object can be captured only. Please file bug .')
  + 'InternalError: Object can capture only once. Please file bug.')
  self._captured = True
  self._object = o
  