Update OrderedCollections requirement from 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 to 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0

Updates the requirements on [OrderedCollections](https://github.com/JuliaCollections/OrderedCollections.jl) to permit the latest version.
- [Release notes](https://github.com/JuliaCollections/OrderedCollections.jl/releases)
- [Commits](JuliaCollections/OrderedCollections.jl@v1.6.0...v2.0.0)

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

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

Author: dependabot[bot]

Project.toml

@@ -20,7 +20,7 @@ StatsFuns = "4c63d2b9-4356-54db-8cca-17b64c39e42c"
 AbstractTrees = "0.3, 0.4"
 Distributions = "0.25"
 OnlineStatsBase = "1.4.7, 1.5, 1.6, 1.7"
-OrderedCollections = "1.1, 1.2, 1.3, 1.4, 1.5, 1.6"
+OrderedCollections = "1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0"
 RecipesBase = "1.1, 1.2, 1.3"
 SpecialFunctions = "2.1, 2.2, 2.3"
 Statistics = "1"