Try py3.8

Despite docker image is for python 3.7, the build command attempts installing huggingface-hub>=0.19, which requires python 3.8.

README.md

@@ -1,5 +1,5 @@
 ---
-python_version: 3.7
+python_version: 3.8
 title: 'Happywhale Demo'
 emoji: 🐬
 colorFrom: green