use `@everywhere ` in distributed bootstrap example

[palday]

As pointed out in #763

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.93%. Comparing base (95a367d) to head (a80a4cd).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #764 +/- ## ======================================= Coverage 96.93% 96.93% ======================================= Files 34 34 Lines 3358 3358 ======================================= Hits 3255 3255 Misses 103 103 ``` | [Flag](https://app.codecov.io/gh/JuliaStats/MixedModels.jl/pull/764/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaStats) | Coverage Δ | | |---|---|---| | [current](https://app.codecov.io/gh/JuliaStats/MixedModels.jl/pull/764/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaStats) | `96.87% <ø> (ø)` | | | [minimum](https://app.codecov.io/gh/JuliaStats/MixedModels.jl/pull/764/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaStats) | `96.83% <ø> (ø)` | | | [nightly](https://app.codecov.io/gh/JuliaStats/MixedModels.jl/pull/764/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaStats) | `96.43% <ø> (+4.07%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaStats#carryforward-flags-in-the-pull-request-comment) to find out more.

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