Fixed test for logistic regression, slope 1.

[gbrsales]

Checks fail with the following log:

1) test: LogisticRegressionTest::test_logistic_regression (F) line: 103 tests/logistic_regression_test.cpp
assertion failed
- Expression: abs(coeffs.at(1)-0.49)<0.01
- Example 2: Slope1 term doesn't match

According to the documentation the expected value for slope 1 is -0.49 and the test should thus have the opposite sign.