Fix sentencepiece version per python version.

docs/installation.md

@@ -21,7 +21,9 @@ Run `conda install -c conda-forge jsonnet=0.15.0` and re-run installation.
 
 * No package 'sentencepiece' found
 
-Run `pip install sentencepiece==0.1.83` and re-run installation.
+Run `pip install sentencepiece==0.1.83` for Python < 3.8 and re-run installation.
+
+Run `pip install sentencepiece==0.1.85` for Python >= 3.8 and re-run installation.
 
 * Missing Cython error
 

setup.py

@@ -10,7 +10,8 @@ REQUIREMENTS = [
     'numpy==1.19.4',
     'overrides==3.1.0',
     'requests==2.23.0',
-    'sentencepiece==0.1.83',
+    'sentencepiece==0.1.83;python_version<"3.8"',
+    'sentencepiece==0.1.85;python_version>="3.8"',
     'spacy==2.3.2',
     'scikit-learn<=0.23.2',
     'torch==1.6.0',