Escape spaces in cmd

[odow]

See here

AmplNLWriter.jl/src/AmplNLWriter.jl

Line 74 in 9e5b590

cmd = `$(solver_path) $(nl_filename) -AMPL $(options)`

x-ref https://discourse.julialang.org/t/issue-parsing-ipopt-jll-string-option-when-there-is-blank-space-in-path/125943

I'm surprised this hasn't come up before