CLI start command's index.html field should wait to load until backen…

[macdonmc]

…d is loaded

Contributing to Twilio

All third-party contributors acknowledge that any contributions they provide will be made under the same open-source license that the open-source project is provided under.

• I acknowledge that all my contributions will be made under the project's license.

[codecov]

Codecov Report

Merging #608 (f8ccfc3) into dev (2a73eed) will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #608      +/-   ##
==========================================
+ Coverage   86.87%   86.95%   +0.08%     
==========================================
  Files         146      147       +1     
  Lines        3686     3710      +24     
  Branches      614      617       +3     
==========================================
+ Hits         3202     3226      +24     
  Misses        387      387              
  Partials       97       97              

Impacted Files	Coverage Δ
packages/flex-plugin-scripts/src/scripts/start.ts	90.57% <ø> (ø)
packages/flex-dev-utils/src/fs.ts	97.30% <100.00%> (+0.15%)	⬆️
...x-plugin-scripts/src/scripts/pre-localrun-check.ts	100.00% <100.00%> (ø)
...ges/flex-plugin-webpack/src/devServer/ipcServer.ts	67.31% <100.00%> (+2.72%)	⬆️
...ges/plugin-flex/src/commands/flex/plugins/start.ts	96.70% <100.00%> (+0.07%)	⬆️

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[theryankennedy]

Looks good! Just one little nitpick