Check for R2017a or older when using jsonencode

[lawrence-mbf]

Motivation

jsonencode doesn't support the keyword arguments used to convert inf or NaN values to null in json, making conversion loops impossible for these versions.

The fixes now will throw a warning on write.

How to test the behavior?

nwbExport(nwb);

Should be successful on MATLAB R2017b and newer and a warning otherwise.

Checklist

• Have you ensured the PR description clearly describes the problem and solutions?
• Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[codecov]

Codecov Report

Merging #464 (69a6498) into master (cd2baec) will decrease coverage by 0.07%.
The diff coverage is 82.14%.

@@            Coverage Diff             @@
##           master     #464      +/-   ##
==========================================
- Coverage   87.61%   87.53%   -0.08%     
==========================================
  Files         127      127              
  Lines        5240     5247       +7     
==========================================
+ Hits         4591     4593       +2     
- Misses        649      654       +5     

Impacted Files	Coverage Δ
+schemes/exportJson.m	90.16% <82.14%> (-7.99%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[bendichter]

looks good to me