message: Fix typo in comment in op_kernel.h
diff: @@ -137,7 +137,7 @@ class OpKernel {
  // op is expensive. The new cost estimate is a weighted average of the old
  // cost estimate and the latest cost.
  void UpdateCostEstimate(uint64 elapsed_cycles) {
  - // N.B. Updates to `cost_estimate_` are atomic but unlocked. Simulataneous
  + // N.B. Updates to `cost_estimate_` are atomic but unlocked. Simultaneous
  // updates may result in one or more updates being ignored. This does not
  // affect correctness but may slow down the update frequency.
  cost_estimate_.store(
  