Warning for dynamic defaults now more annoying than helpful

[yanokwa]

Closes #523

Why is this the best possible solution? Were any other approaches considered?

Narrowest fix possible

What are the regression risks?

No major ones.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

No.

Before submitting this PR, please make sure you have:

• [x] included test cases for core behavior and edge cases in tests_v1
• [x] run nosetests and verified all tests pass
• [x] run black pyxform to format code
• [x] verified that any code or assets from external sources are properly credited in comments

[codecov-io]

Codecov Report

Merging #526 (a9def04) into master (bee9654) will decrease coverage by 0.07%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #526      +/-   ##
==========================================
- Coverage   83.92%   83.84%   -0.08%     
==========================================
  Files          25       23       -2     
  Lines        3713     3554     -159     
  Branches      865      834      -31     
==========================================
- Hits         3116     2980     -136     
+ Misses        452      431      -21     
+ Partials      145      143       -2     

Impacted Files	Coverage Δ
pyxform/xls2json.py	78.52% <ø> (-0.13%)	:arrow_down:
pyxform/__init__.py
pyxform/utils.py

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update bee9654...a9def04. Read the comment docs.