Set default weight factor to 1

[aadityasaraiya]

Hey,

I have set the default weight factor for the position constraint for the link sensor_constraint_frame. This is to avoid the unnecessary warning which comes up when this isn't done.

[ WARN] [1530883644.819044064, 925.199000000]: The weight on position constraint for link 'sensor_constraint_frame' is near zero. Setting to 1.0.

The weight in this case, being the weighting factor for this constraint (denotes relative importance to other constraints. Closer to zero means less important) as shown in this code.