correct extension for logo

Author: valeriupredoi

README.md

@@ -3,7 +3,7 @@
 [![Test](https://github.com/NCAS-CMS/pyfive/actions/workflows/pytest.yml/badge.svg)](https://github.com/NCAS-CMS/pyfive/actions/workflows/pytest.yml)
 [![codecov](https://codecov.io/gh/NCAS-CMS/pyfive/graph/badge.svg?token=3In5JuzeGK)](https://codecov.io/gh/NCAS-CMS/pyfive)
 
-![pyfive-logo](https://github.com/NCAS-CMS/pyfive/blob/main/doc/figures/Pyfive-logo.jpg)
+![pyfive-logo](https://github.com/NCAS-CMS/pyfive/blob/main/doc/figures/Pyfive-logo.png)
 
 pyfive : A pure Python HDF5 file reader
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