Fix import errors introduces by sklearn 0.1.5

With sklearn version 0.1.5 the check_pandas_support function has been
moved to util._optional_dependencies. This has been adapted in our code.

src/skmatter/datasets/_base.py

@@ -1,7 +1,14 @@
 from os.path import dirname, join
 
 import numpy as np
-from sklearn.utils import Bunch, check_pandas_support
+
+import skmatter
+
+
+if skmatter.__version__ >= "0.1.5":
+    from utils._optional_dependencies import check_pandas_support
+else:
+    from sklearn.utils import Bunch, check_pandas_support
 
 
 def load_nice_dataset():