message: Fix error message
  Reviewers: #tensorflow, georgep, davidn
diff: @@ -618,8 +618,8 @@ Status PipelineVisitor::FinishVisit(HloInstruction* inst) {
  Status PipelineVisitor::HandleTuple(HloInstruction* hlo) {
  if (hlo->parent()->root_instruction() != hlo) {
  return FailedPrecondition(
  - "Hlo tuple instructions are only allow in a pipeline when they are the "
  - "root instruction. Hlo instruction \"%s\" is not.",
  + "Hlo tuple instructions are only allowed in a pipeline when they are "
  + "the root instruction. Hlo instruction \"%s\" is not.",
  hlo->name());
  }
  