Change variance_threshold default to 0.01

[shntnu]

Description

From: #282

I noticed that variance_threshold always had unique_cut=0.01 as a default, while feature_select later set more strict default unique_cut=0.1, overriding that of variance_threshold.

The threshold of 0.1 is too high; I think we should change the default to 0.01. This might be a breaking change of sorts but this might be the right time to do it (given the upcoming v1.0.0).

What is the nature of your change?

• Bug fix (fixes an issue).
• Enhancement (adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• This change requires a documentation update.

Checklist

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• I have read the CONTRIBUTING.md guidelines.
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[codecov-commenter]

Codecov Report

Merging #286 (ee24fef) into master (182745a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #286   +/-   ##
=======================================
  Coverage   95.12%   95.12%           
=======================================
  Files          57       57           
  Lines        3057     3057           
=======================================
  Hits         2908     2908           
  Misses        149      149           

Flag	Coverage Δ
unittests	95.12% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pycytominer/feature_select.py	94.44% <ø> (ø)
pycytominer/operations/variance_threshold.py	97.05% <ø> (ø)

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