Update version of Matplotlib that needs Python 3.7

hs2361 · web-flow · commit e6748cb8edea · 2020-11-04T14:14:35.000+05:30
Fixes #18882. Updated the minimum version of Matplotlib from 3.1 to 3.4 in setup.py.
diff --git a/setup.py b/setup.py
@@ -12,7 +12,7 @@
 
 if sys.version_info < min_version:
     error = """
-Beginning with Matplotlib 3.1, Python {0} or above is required.
+Beginning with Matplotlib 3.4, Python {0} or above is required.
 You are using Python {1}.
 
 This may be due to an out of date pip.
