Replace ZeroVector with Zeros from FillArrays

[devmotion]

Fixes #833.

[codecov-io]

Codecov Report

Merging #1020 into master will increase coverage by 0.02%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##           master    #1020      +/-   ##
==========================================
+ Coverage   77.92%   77.95%   +0.02%     
==========================================
  Files         112      112              
  Lines        5391     5362      -29     
==========================================
- Hits         4201     4180      -21     
+ Misses       1190     1182       -8

Impacted Files	Coverage Δ
src/Distributions.jl	100% <ø> (ø)	⬆️
src/multivariate/mvnormal.jl	71.59% <100%> (ø)	⬆️
src/multivariate/mvtdist.jl	59.78% <100%> (ø)	⬆️
src/multivariate/mvlognormal.jl	96.82% <100%> (ø)	⬆️
src/multivariate/mvnormalcanon.jl	78.72% <66.66%> (-2.13%)	⬇️
src/utils.jl	80% <83.33%> (+6.53%)	⬆️

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[matbesancon]

Could you add a compat entry for FillArrays at 0.8 in the Project.toml?

[matbesancon]

Cool, merging as soon as this shows green, thank you for this