CompatHelper: bump compat for "ProtoBuf" to "0.9"

[github-actions]

This pull request changes the compat entry for the ProtoBuf package from 0.7, 0.8 to 0.7, 0.8, 0.9.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[NHDaly]

This broke the build. Perhaps the ProtoBuf API has changed. (Compat bounds are pretty cool! They save users from a broken system when they run pkg update! cool! 😁)

empty output: Error During Test at /Users/travis/build/JuliaPerf/PProf.jl/test/PProf.jl:22
  Test threw exception
  Expression: begin
    pprof(out=out, web=false)
    true
end
  UndefVarError: fillunset not defined
  Stacktrace:
   [1] (::PProf.perftools.profiles.var"#ValueType#1#2")(::Base.Iterators.Pairs{Symbol,Int64,Tuple{Symbol,Symbol},NamedTuple{(:_type, :unit),Tuple{Int64,Int64}}}, ::Type{PProf.perftools.profiles.ValueType}) at /Users/travis/build/JuliaPerf/PProf.jl/lib/profile_pb.jl:9
   [2] (::Core.var"#kw#Type")(::NamedTuple{(:_type, :unit),Tuple{Int64,Int64}}, ::Type{PProf.perftools.profiles.ValueType}) at ./none:0
   [3] (::PProf.var"#ValueType!#4")(::String, ::String) at /Users/travis/build/JuliaPerf/PProf.jl/src/PProf.jl:124
   [4] #pprof#1(::Nothing, ::Bool, ::String, ::Int64, ::String, ::Bool, ::Bool, ::Nothing, ::Nothing, ::Bool, ::typeof(PProf.pprof), ::Nothing, ::Nothing) at /Users/travis/build/JuliaPerf/PProf.jl/src/PProf.jl:136
   [5] (::PProf.var"#kw##pprof")(::NamedTuple{(:out, :web),Tuple{String,Bool}}, ::typeof(PProf.pprof), ::Nothing, ::Nothing) at ./none:0 (repeats 2 times)
   [6] top-level scope at /Users/travis/build/JuliaPerf/PProf.jl/test/PProf.jl:22
   [7] top-level scope at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.3/Test/src/Test.jl:1107
   [8] top-level scope at /Users/travis/build/JuliaPerf/PProf.jl/test/PProf.jl:19