update deprecated calls to Buffer()

[msimerson]

Fixes #2374

Changes proposed in this pull request:

Checklist:

• docs updated
• tests updated
• Changes updated

[codecov]

Codecov Report

Merging #2553 into master will decrease coverage by 0.02%.
The diff coverage is 56.66%.

@@            Coverage Diff             @@
##           master    #2553      +/-   ##
==========================================
- Coverage   59.45%   59.42%   -0.03%     
==========================================
  Files          28       28              
  Lines        6200     6199       -1     
  Branches     1543     1542       -1     
==========================================
- Hits         3686     3684       -2     
- Misses       2514     2515       +1

Impacted Files	Coverage Δ
server.js	38.66% <0%> (-0.21%)	⬇️
transaction.js	88.52% <100%> (ø)	⬆️
messagestream.js	71.95% <25%> (ø)	⬆️
chunkemitter.js	59.57% <33.33%> (ø)	⬆️
mailheader.js	86.45% <50%> (ø)	⬆️
dkim.js	75.15% <66.66%> (ø)	⬆️
mailbody.js	83.46% <70%> (ø)	⬆️
connection.js	50.83% <75%> (-0.04%)	⬇️

---

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[codecov]

Codecov Report

Merging #2553 into master will decrease coverage by <.01%.
The diff coverage is 59.25%.

@@            Coverage Diff             @@
##           master    #2553      +/-   ##
==========================================
- Coverage   59.45%   59.44%   -0.01%     
==========================================
  Files          28       28              
  Lines        6200     6197       -3     
  Branches     1543     1542       -1     
==========================================
- Hits         3686     3684       -2     
+ Misses       2514     2513       -1

Impacted Files	Coverage Δ
transaction.js	88.52% <100%> (ø)	⬆️
messagestream.js	71.95% <25%> (ø)	⬆️
chunkemitter.js	59.57% <33.33%> (ø)	⬆️
mailheader.js	86.45% <50%> (ø)	⬆️
connection.js	50.83% <66.66%> (-0.04%)	⬇️
dkim.js	75.15% <66.66%> (ø)	⬆️
mailbody.js	83.46% <70%> (ø)	⬆️

---

Continue to review full report at Codecov.

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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