Bump Keras requirement to >=2.2.5

mhcflurry/version.py

-__version__ = "1.3.0"
+__version__ = "1.3.1"

requirements.txt

 six
 numpy>=1.11
 pandas>=0.20.3
-Keras>=2.0.9
+Keras>=2.2.5
 tensorflow>=1.1.0
 appdirs
 scikit-learn
 mhcnames
 pyyaml
 tqdm
-np_utils
\ No newline at end of file
+np_utils

setup.py

@@ -51,7 +51,7 @@ if __name__ == '__main__':
         'six',
         'numpy>=1.11',
         'pandas>=0.20.3',
-        'Keras>=2.0.9',
+        'Keras>=2.2.5',
         'appdirs',
         'tensorflow>=1.1.0',
         'scikit-learn',