Limit SciPy 1.6.0 for Python 3.6.

setup.py

@@ -12,6 +12,7 @@ REQUIREMENTS = [
     'requests==2.23.0',
     'sentencepiece==0.1.83;python_version<"3.8"',
     'sentencepiece==0.1.85;python_version>="3.8"',
+    'scipy<1.6.0;python_version<"3.7"',  # SciPy 1.6.0 works for 3.7+
     'spacy==2.3.2',
     'scikit-learn<=0.23.2',
     'torch==1.6.0',