Bump version to v0.3.15

[codecov[bot]]

Codecov Report

Patch coverage: 75.00% and project coverage change: -0.14 :warning:

Comparison is base (bbca283) 60.95% compared to head (69a13fb) 60.81%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #82 +/- ## ========================================== - Coverage 60.95% 60.81% -0.14% ========================================== Files 14 14 Lines 1045 1049 +4 ========================================== + Hits 637 638 +1 - Misses 408 411 +3 ``` | [Impacted Files](https://codecov.io/gh/JuliaApproximation/ApproxFunFourier.jl/pull/82?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation) | Coverage Δ | | |---|---|---| | [src/ApproxFunFourier.jl](https://codecov.io/gh/JuliaApproximation/ApproxFunFourier.jl/pull/82?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL0FwcHJveEZ1bkZvdXJpZXIuamw=) | `65.57% <ø> (-0.41%)` | :arrow_down: | | [src/LaurentOperators.jl](https://codecov.io/gh/JuliaApproximation/ApproxFunFourier.jl/pull/82?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL0xhdXJlbnRPcGVyYXRvcnMuamw=) | `67.09% <25.00%> (-1.30%)` | :arrow_down: | | [src/Domains/Circle.jl](https://codecov.io/gh/JuliaApproximation/ApproxFunFourier.jl/pull/82?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL0RvbWFpbnMvQ2lyY2xlLmps) | `65.95% <100.00%> (+0.74%)` | :arrow_up: | | [src/FourierOperators.jl](https://codecov.io/gh/JuliaApproximation/ApproxFunFourier.jl/pull/82?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL0ZvdXJpZXJPcGVyYXRvcnMuamw=) | `77.03% <100.00%> (+0.33%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation)

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