Fix #2669 & #2396 - Failure to start Neovim on OSX 10.14 Mojave

[bryphe]

Issue: Oni was hitting neovim/neovim#9134 when launched from finder in OSX Mojave, causing Neovim not to load.

Defect: Prior to the fix in Neovim, if the LANG environment variable was not set in OSX, Neovim would crash. Resiliency on the Neovim side is added here: neovim/neovim@57acfce

Fix: For now - we'll just set a default (overridable) value in the case where LANG is not set. Once we pick up the 0.3.2 binaries, we won't need that anymore.

Fixes #2669 & #2396

[codecov]

Codecov Report

Merging #2682 into master will decrease coverage by <.01%.
The diff coverage is 25%.

@@            Coverage Diff             @@
##           master    #2682      +/-   ##
==========================================
- Coverage   45.78%   45.78%   -0.01%     
==========================================
  Files         361      361              
  Lines       14630    14634       +4     
  Branches     1924     1926       +2     
==========================================
+ Hits         6699     6700       +1     
- Misses       7701     7703       +2     
- Partials      230      231       +1

Impacted Files	Coverage Δ
...src/Services/Configuration/DefaultConfiguration.ts	87.5% <ø> (ø)	⬆️
browser/src/Plugins/Api/Process.ts	52.63% <25%> (-1.54%)	⬇️

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