softer requirements for external packages versions (#388)

requirements.txt

@@ -1,19 +1,19 @@
 numpy>=1.20.0
-pandas==1.2.0
-scipy==1.6.1
-scikit-learn==0.24.2
-xgboost==1.3.3
-lightgbm==3.0.0
-catboost==0.24.4
-joblib==1.0.1
+pandas>=1.2.0
+scipy>=1.6.1
+scikit-learn>=0.24.2
+xgboost>=1.3.3
+lightgbm>=3.0.0
+catboost>=0.24.4
+joblib>=1.0.1
 pyarrow>=2.0.0
-tabulate==0.8.7
+tabulate>=0.8.7
 matplotlib>=3.2.2
-dtreeviz==1.3
-shap==0.36.0
-seaborn==0.11.1
-wordcloud==1.8.1
-category_encoders==2.2.2
-optuna==2.7.0
+dtreeviz>=1.3
+shap>=0.36.0
+seaborn>=0.11.1
+wordcloud>=1.8.1
+category_encoders>=2.2.2
+optuna>=2.7.0
 scikit-plot==0.3.7
 markdown