Fix for d3.v5

[masayuki0812]

I checked every sample in htdocs/samples and looks working.

Closes #2319

[kt3k]

I agree with this change. Should we bump minor version (+0.1.0) or patch version (+0.0.1) after merging this?

I think we need to update getting started guide's D3 version as well. (That document is now in this repository, migrated from c3js/c3js.org)

[panthony]

D3 5.0 introduces only a few non-backwards-compatible changes.

@kt3k I'd say minor at least... shouldn't introduce breaking changes on a patch version.

[codecov-io]

Codecov Report

Merging #2335 into master will increase coverage by 0.03%.
The diff coverage is 20%.

@@            Coverage Diff             @@
##           master    #2335      +/-   ##
==========================================
+ Coverage   77.12%   77.15%   +0.03%     
==========================================
  Files          51       51              
  Lines        4131     4124       -7     
==========================================
- Hits         3186     3182       -4     
+ Misses        945      942       -3

Impacted Files	Coverage Δ
src/data.convert.js	88.63% <20%> (+1.58%)	⬆️

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[kt3k]

Released as v0.6.0 https://github.com/c3js/c3/releases/tag/v0.6.0 🎉