make HyperDualNumbers.jl a weak dependency

[ranocha]

179 made HyperDualNumbers.jl a strong (?) dependency for all Julia versions. I turned it into a weak dependency (for new versions of Julia).

I also increased the version number of Octavian.jl.

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.09 :warning:

Comparison is base (a37ae26) 90.40% compared to head (f4577bb) 90.31%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #180 +/- ## ========================================== - Coverage 90.40% 90.31% -0.09% ========================================== Files 14 14 Lines 1146 1146 ========================================== - Hits 1036 1035 -1 - Misses 110 111 +1 ``` | [Impacted Files](https://app.codecov.io/gh/JuliaLinearAlgebra/Octavian.jl/pull/180?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaLinearAlgebra) | Coverage Δ | | |---|---|---| | [src/Octavian.jl](https://app.codecov.io/gh/JuliaLinearAlgebra/Octavian.jl/pull/180?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaLinearAlgebra#diff-c3JjL09jdGF2aWFuLmps) | `100.00% <ø> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/JuliaLinearAlgebra/Octavian.jl/pull/180/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaLinearAlgebra)

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[chriselrod]

Oops, I should have looked at that PR more closely.