NODE_NO_READLINE support

[cspotcode]

https://nodejs.org/api/repl.html#repl_using_the_node_js_repl_with_advanced_line_editors

Totally untested; just wanted to jot this down before I forget. EDIT: Does it need tests? If so I'll add then, but it's so minor.
#328

[codecov]

Codecov Report

Merging #1090 into master will increase coverage by 0.12%.
The diff coverage is 0.00%.

@@ Coverage Diff @@## master #1090 +/- ##
==========================================
+ Coverage 75.08% 75.20% +0.12% 
==========================================
Files 6 6 Lines 606 613 +7 Branches 141 143 +2 ==========================================
+ Hits 455 461 +6 
Misses 100 100 - Partials 51 52 +1 

Flag	Coverage Δ
#node_10	71.95% <0.00%> (-0.40%)	⬇️
#node_12_15	72.34% <0.00%> (-0.41%)	⬇️
#node_12_16	72.34% <0.00%> (-0.41%)	⬇️
#node_13	74.87% <0.00%> (+0.12%)	⬆️
#node_14	74.87% <0.00%> (+0.12%)	⬆️
#typescript_2_7	74.71% <0.00%> (+0.12%)	⬆️
#typescript_latest	73.89% <0.00%> (+0.13%)	⬆️
#typescript_next	73.73% <0.00%> (+0.13%)	⬆️
#ubuntu	74.87% <0.00%> (+0.12%)	⬆️
#windows	75.04% <0.00%> (+0.12%)	⬆️

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Impacted Files	Coverage Δ
src/bin.ts	70.11% <0.00%> (-0.41%)	⬇️
src/index.ts	77.64% <0.00%> (+0.40%)	⬆️

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[coveralls]

Coverage increased (+1.2%) to 83.163% when pulling b65c761 on ab/node_no_readline into 04e7896 on master.