fix pd concat axis=0 in 1 more place

Author: DarnellGranberry

topaz/utils/data/train_test_split_micrographs.py

@@ -40,8 +40,8 @@ def train_test_split_micrographs(seed, n, path, format, image_dir, file_ext):
         image_names_train.append(image_names[j])
         groups_train.append(groups[j])
 
-    targets_train = pd.concat(groups_train, 0)
-    targets_test = pd.concat(groups_test, 0)
+    targets_train = pd.concat(groups_train, axis=0)
+    targets_test = pd.concat(groups_test, axis=0)
 
 
     ## if the image-dir is specified, make the image list files