Update reco.requirements.txt

Author: dciborow

ai-python/msft/reco.requirements.txt

@@ -12,7 +12,7 @@ nltk>=3.4,<4
 pydocumentdb>=2.3.3<3
 pymanopt>=0.2.5,<1
 seaborn==0.11.1
-transformers>=2.5.0,<5
+transformers==4.9.0
 bottleneck>=1.2.1,<2
 category_encoders>=1.3.0,<2
 jinja2>=2,<3