Update StatsFuns requirement from 1.0, 1.1, 1.2, 1.3 to 1.0, 1.1, 1.2, 1.3, 2.0

Updates the requirements on [StatsFuns](https://github.com/JuliaStats/StatsFuns.jl) to permit the latest version.
- [Release notes](https://github.com/JuliaStats/StatsFuns.jl/releases)
- [Commits](JuliaStats/StatsFuns.jl@v1.3.0...v2.0.0)

---
updated-dependencies:
- dependency-name: StatsFuns
  dependency-version: 2.0.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Project.toml

@@ -25,7 +25,7 @@ RecipesBase = "1.1, 1.2, 1.3"
 SpecialFunctions = "2.1, 2.2, 2.3"
 Statistics = "1"
 StatsBase = "0.32, 0.33, 0.34"
-StatsFuns = "1.0, 1.1, 1.2, 1.3"
+StatsFuns = "1.0, 1.1, 1.2, 1.3, 2.0"
 julia = "1.0"
 
 [extras]