set default gear ratio to 0

Author: petercorke

roboticstoolbox/robot/Link.py

@@ -95,7 +95,7 @@ def __init__(
             Jm=0.0,
             B=0.0,
             Tc=np.zeros((2,)),
-            G=1.0,
+            G=0.0,
             mesh=None,
             geometry=[],
             collision=[],