Swap Accel and Gyro where angular_velocity and linear_acceleration are set

msg_imu.angular_velocity.* should be equal to msg_in.Gyro.*, NOT msg_in.Accel. Likewise for msg_imu.linear_acceleration.*. These are swapped by mistake.
Merge pull request #4 from acarrillo/master

Swap Accel and Gyro where angular_velocity and linear_acceleration are set