Add scikit-learn as required install

setup.py

@@ -12,7 +12,7 @@ setuptools.setup(
     long_description=long_description,
     long_description_content_type="text/markdown",
     url="https://github.com/MilesCranmer/pysr",
-    install_requires=["julia", "numpy", "pandas", "sympy"],
+    install_requires=["julia", "numpy", "pandas", "sympy", "scikit-learn"],
     packages=setuptools.find_packages(),
     package_data={"pysr": ["../Project.toml", "../datasets/*"]},
     include_package_data=False,