Add py2 compatibility imports to kernels/__init__.py
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
from .kernel import Kernel, AdditiveKernel, ProductKernel
from .rbf_kernel import RBFKernel
from .matern_kernel import MaternKernel
