fix python ver for matplotlib, test=develop (#18123)

update config for matplotlib, because python 3.6 is required by 3.1+

python/requirements.txt

@@ -2,10 +2,10 @@ requests>=2.20.0
 numpy>=1.12
 protobuf>=3.1.0
 recordio>=0.1.0
-matplotlib<=2.2.3 ; python_version<"3.5"
+matplotlib<=2.2.4 ; python_version<"3.6"
 scipy>=0.19.0, <=1.2.1 ; python_version<"3.5"
 nltk>=3.2.2, <=3.4 ; python_version<"3.5"
-matplotlib ; python_version>="3.5"
+matplotlib ; python_version>="3.6"
 scipy ; python_version>="3.5"
 nltk ; python_version>="3.5"
 rarfile