feat: explicit electron export target

[kasinskas]

Description

Specify target platform in electron-builder command (https://www.electron.build/cli) to enable building other platforms, because "without target configuration, electron-builder builds Electron app for current platform and current architecture using default target", so on a mac even if i run rnv export -p windows I get mac build in a windows folder

Breaking Changes

• PRs should not introduce breaking changes to existing functionality
• if breaking change cannot be avoided it has to be introduced in 2 phases (release cycles of 0.x.0)
  • 0.x.0 Add new functionality + add DEPRECATED warning to existing fuctionality
  • 0.[x+1].0 Remove deprecated functionality

I have tested my changes on:

ReNative project directly:

• ios simulator
• ios device
• android simulator
• android device
• web browser
• web -e next browser
• tvos simulator
• tvos device
• androidtv simulator
• androidtv device
• androidwear simulator
• androidwear device
• tizen simulator
• tizen device
• tizenmobile simulator
• tizenwatch device
• webos simulator
• webos device
• macos
• windows
• chromecast device

New project:

• ios simulator
• ios device
• android simulator
• android device
• web browser
• web -e next browser
• tvos simulator
• tvos device
• androidtv simulator
• androidtv device
• androidwear simulator
• androidwear device
• tizen simulator
• tizen device
• tizenmobile simulator
• tizenwatch device
• webos simulator
• webos device
• macos
• windows
• chromecast device

Existing Project created with previous version of renative:

• ios simulator
• ios device
• android simulator
• android device
• web browser
• web -e next browser
• tvos simulator
• tvos device
• androidtv simulator
• androidtv device
• androidwear simulator
• androidwear device
• tizen simulator
• tizen device
• tizenmobile simulator
• tizenwatch device
• webos simulator
• webos device
• macos
• windows
• chromecast device

[codecov-commenter]

Codecov Report

Merging #753 (e7525eb) into develop (5260998) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #753   +/-   ##
========================================
  Coverage    19.88%   19.88%           
========================================
  Files           85       85           
  Lines         5883     5883           
  Branches      1332     1332           
========================================
  Hits          1170     1170           
  Misses        3515     3515           
  Partials      1198     1198           

Flag	Coverage Δ
rnvunittests	19.88% <ø> (ø)

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