fix issue on GeneralDichotomy initial weights

[smbct]

This commit solves an issue on the weight update procedure in GeneralDichotomy.
Initial weights could be previously wrongly updated, which makes the bensolve vlp instance test fails (http://www.bensolve.org/).

The method should be able to find at least the four upper image points:

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.64%. Comparing base (b71397a) to head (0fa92ef).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #208      +/-   ##
==========================================
- Coverage   99.64%   99.64%   -0.01%     
==========================================
  Files          15       15              
  Lines        1421     1414       -7     
==========================================
- Hits         1416     1409       -7     
  Misses          5        5              

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[odow]

I don't know the algorithm well enough to notice these sorts of details. But in my experience, you cannot have too many test cases!