Fix typos like Unitful.EnergyUnit in docs

[singularitti]

Unitful.EnergyUnit, Unitful.LengthUnit & Unitful.MassUnit were deprecated long time ago. I suppose them to have s at the end.

[codecov-commenter]

Codecov Report

Merging #381 into master will decrease coverage by 0.16%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #381      +/-   ##
==========================================
- Coverage   83.33%   83.16%   -0.17%     
==========================================
  Files          15       15              
  Lines        1284     1283       -1     
==========================================
- Hits         1070     1067       -3     
- Misses        214      216       +2     

Impacted Files	Coverage Δ
src/logarithm.jl	69.16% <0.00%> (-0.84%)	⬇️
src/quantities.jl	94.09% <0.00%> (-0.03%)	⬇️

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[giordano]

Thanks!