Update NLsolve requirement to 4.5.1 in /docs

Updates the requirements on [NLsolve](https://github.com/JuliaNLSolvers/NLsolve.jl) to permit the latest version.
- [Release notes](https://github.com/JuliaNLSolvers/NLsolve.jl/releases)
- [Commits](JuliaNLSolvers/NLsolve.jl@v0.1.0...v4.5.1)

---
updated-dependencies:
- dependency-name: NLsolve
  dependency-version: 4.5.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

docs/Project.toml

@@ -16,3 +16,4 @@ Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 
 [compat]
 Documenter = "1.3"
+NLsolve = "4.5.1"