bump ColorSchemes.jl dependency due to precompile

[Byrth]

ColorScheme is not parameterized (as in lines 5 and 7 of src/precompile.jl) until v3.8, so this causes an error on load for Julia >=v1.4.2 in projects that are restricting ColorSchemes to 3.7.

Error looks like:

ERROR: LoadError: TypeError: in Type{...} expression, expected UnionAll, got Type{ColorSchemes.ColorScheme}
Stacktrace:
 [1] _precompile_() at /root/.julia/packages/PlotUtils/3Ttrk/src/precompile.jl:5
 [2] top-level scope at /root/.julia/packages/PlotUtils/3Ttrk/src/PlotUtils.jl:44
 [3] include(::Function, ::Module, ::String) at ./Base.jl:380
 [4] include(::Module, ::String) at ./Base.jl:368
 [5] top-level scope at none:2
 [6] eval at ./boot.jl:331 [inlined]
 [7] eval(::Expr) at ./client.jl:467
 [8] top-level scope at ./none:3
in expression starting at /root/.julia/packages/PlotUtils/3Ttrk/src/PlotUtils.jl:42
ERROR: Failed to precompile PlotUtils [995b91a9-d308-5afd-9ec6-746e21dbc043] to /root/.julia/compiled/v1.5/PlotUtils/YveHG_XgY6Z.ji.
Stacktrace:
 [1] error(::String) at ./error.jl:33
 [2] compilecache(::Base.PkgId, ::String) at ./loading.jl:1305
 [3] _require(::Base.PkgId) at ./loading.jl:1030
 [4] require(::Base.PkgId) at ./loading.jl:928
 [5] require(::Module, ::Symbol) at ./loading.jl:923

[ranocha]

I get the same error. Currently, some Julia installations are forced to use ColorSchemes v3.7 since its version bounds for StaticArrays.jl are not updated yet to v1.0, see JuliaGraphics/ColorSchemes.jl#53.