FIX: hyperplane: Incorrectly throwing out stable starting points

[richardotis]

Fixes #427

[codecov]

Codecov Report

Merging #428 (12209f7) into develop (04b870e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #428   +/-   ##
========================================
  Coverage    90.24%   90.25%           
========================================
  Files           50       50           
  Lines         7723     7726    +3     
========================================
+ Hits          6970     6973    +3     
  Misses         753      753           

Impacted Files	Coverage Δ
pycalphad/core/hyperplane.pyx	93.33% <100.00%> (-0.35%)	⬇️
pycalphad/tests/test_equilibrium.py	98.44% <100.00%> (+0.02%)	⬆️

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[bocklund]

I re-ran the ternary example, it seems fixed and significantly faster. In fact, I was getting an error on develop, some Gibbs phase rule violation in array sizes, I believe.

master branch (4m44s runtime):

12209f7 (0m31s runtime):

I honestly don't know how this slipped by for so long.