Bump transformers from 2.5.1 to 4.30.0 in /examples/onnx/gpt2

Bumps [transformers](https://github.com/huggingface/transformers) from 2.5.1 to 4.30.0.
- [Release notes](https://github.com/huggingface/transformers/releases)
- [Commits](https://github.com/huggingface/transformers/compare/v2.5.1...v4.30.0)

---
updated-dependencies:
- dependency-name: transformers
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/examples/onnx/gpt2/requirements.txt b/examples/onnx/gpt2/requirements.txt
index 14693ad..0e6bb6b 100644
--- a/examples/onnx/gpt2/requirements.txt
+++ b/examples/onnx/gpt2/requirements.txt
@@ -1 +1 @@
-transformers==2.5.1
\ No newline at end of file
+transformers==4.30.0
\ No newline at end of file