leg probabilities are different between Kinetic and Melodic

[s-kodama-isp]

We found that detected results by leg_detector are different between Kinetic and Melodic in our internal test.
It looked that bugs pointed out in #67 about leg probabilities remain in the Melodic version. We think that the probability calculation in leg_detector.cpp(L735-737) is wrong.

people/leg_detector/src/leg_detector.cpp

Lines 735 to 737 in bc73fa0

	float probability = 0.5 -
	forest->predict(tmp_mat, cv::noArray(), cv::ml::RTrees::PREDICT_SUM) /
	forest->getRoots().size();

As results, probabilities take values between -0.5 and 1.5.

So, we want to fix as below.

float probability = 0.5 + 0.5 *
	static_cast<float>(forest->predict(tmp_mat, cv::noArray(), cv::ml::RTrees::PREDICT_SUM)) /
	static_cast<float>(forest->getRoots().size());

After we fixed this bug as the above, we got almost the same results between Kinetic and Melodic in our internal test.
We will create a pull request. Thanks.