fix: min pytest version

Author: mgxd

setup.cfg

@@ -10,7 +10,7 @@ install_requires =
     nibabel
     h5py
 test_requires =
-    pytest
+    pytest >= 4.4.0
     pytest-cov
     pytest-xdist
     nose
@@ -20,7 +20,7 @@ include_package_data = True
 
 [options.extras_require]
 test =
-    pytest
+    pytest >= 4.4.0
     pytest-cov
     pytest-xdist
     nose