Enforce optionality of mujoco

Author: LemonPi

src/pytorch_kinematics/__init__.py

@@ -1,6 +1,10 @@
 from pytorch_kinematics.sdf import *
 from pytorch_kinematics.urdf import *
-from pytorch_kinematics.mjcf import *
+
+try:
+    from pytorch_kinematics.mjcf import *
+except ImportError:
+    pass
 from pytorch_kinematics.transforms import *
 from pytorch_kinematics.chain import *
-from pytorch_kinematics.ik import *
+from pytorch_kinematics.ik import *