auto -> return type for C++11 support

Summary: Builds are breaking https://travis-ci.org/caffe2/caffe2/jobs/228149040

Reviewed By: Yangqing

Differential Revision: D4992774

fbshipit-source-id: bea4132db9c2bf24342887a2bc4cbd6225a5ce9a
diff --git a/caffe2/queue/rebatching_queue.cc b/caffe2/queue/rebatching_queue.cc
index 0cf5e19..07a5d15 100644
--- a/caffe2/queue/rebatching_queue.cc
+++ b/caffe2/queue/rebatching_queue.cc
@@ -63,7 +63,9 @@
   }
 }
 
-auto split(CPUContext& context, const std::vector<const TensorCPU*>& inputs) {
+std::vector<std::vector<TensorCPU>> split(
+    CPUContext& context,
+    const std::vector<const TensorCPU*>& inputs) {
   CAFFE_ENFORCE(!inputs.empty());
 
   const auto outputSize = inputs[0]->dims().at(0);