Allow warnings in the minimum build

skimage/_shared/testing.py

@@ -190,7 +190,8 @@ def setup_test():
     from scipy.io import loadmat
     from skimage import viewer, filter
     np.random.seed(0)
-    warnings.simplefilter('error') 
+    if os.environ.get('TRAVIS_PYTHON_VERSION', None) != '2.7':
+        warnings.simplefilter('error') 
 
 
 def teardown_test():