Hooks: Use public get_data_path in matplotlib hook.

Private _get_data_path was removed in matplotlib-3.4.0rc1.
This change simply removes the underscore to use the public
version. (#5567)

PyInstaller/hooks/hook-matplotlib.py

@@ -13,7 +13,7 @@
 from PyInstaller.utils.hooks import exec_statement
 
 mpl_data_dir = exec_statement(
-    "import matplotlib; print(matplotlib._get_data_path())")
+    "import matplotlib; print(matplotlib.get_data_path())")
 
 datas = [
     (mpl_data_dir, "matplotlib/mpl-data"),