node: remove 6, add 11,12

[msimerson]

• probably worked in node 12.2
• broken in 12.3 due to this bug
• will probably work again after 12.3.1

[msimerson]

• wait for 12.3.1 to be released
• re-run Travis tests
• if success, merge

[codecov]

Codecov Report

Merging #2650 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2650      +/-   ##
==========================================
+ Coverage   59.69%   59.73%   +0.03%     
==========================================
  Files          29       29              
  Lines        6387     6387              
  Branches     1587     1587              
==========================================
+ Hits         3813     3815       +2     
+ Misses       2574     2572       -2

Impacted Files	Coverage Δ
server.js	40.59% <0%> (+0.53%)	⬆️

---

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[codecov]

Codecov Report

Merging #2650 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2650      +/-   ##
==========================================
+ Coverage   59.69%   59.73%   +0.03%     
==========================================
  Files          29       29              
  Lines        6387     6387              
  Branches     1587     1587              
==========================================
+ Hits         3813     3815       +2     
+ Misses       2574     2572       -2

Impacted Files	Coverage Δ
server.js	40.59% <0%> (+0.53%)	⬆️

---

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 b117e55...8777585. Read the comment docs.