fix jacobi evaluation

[jishnub]

After this PR, the following works:

julia> f = Fun(Jacobi(0,0), Float64[1,2,3])
Fun(Legendre(), [1.0, 2.0, 3.0])

julia> Evaluation(1) * f
6.0 on Point(1)

[codecov]

Codecov Report

Merging #90 (ea444d9) into master (987df98) will increase coverage by 0.28%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
+ Coverage   57.62%   57.91%   +0.28%     
==========================================
  Files          27       27              
  Lines        2414     2414              
==========================================
+ Hits         1391     1398       +7     
+ Misses       1023     1016       -7     

Impacted Files	Coverage Δ
src/Spaces/Jacobi/JacobiOperators.jl	57.46% <100.00%> (+2.27%)	⬆️
src/specialfunctions.jl	68.88% <0.00%> (-2.23%)	⬇️
src/Spaces/Jacobi/Jacobi.jl	57.42% <0.00%> (+0.99%)	⬆️

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