Latest version doesn't work, likely about the Project file?

Hi,

PyPlot stopped working for me (after some upgrade/downgrade?) and I was on master so I made sure to use Julia 1.5.1, and had to downgrade to get it working:

$ ~/julia-1.5.1/bin/julia --startup-file=no -q
julia> using PyPlot
[ Info: Precompiling PyPlot [d330b81b-6aea-500a-939a-2ce795aea3ee]

$ ~/julia-1.5.1/bin/julia --startup-file=no -q
(@v1.5) pkg> add PyPlot@v2.9.0
Updating registry at `~/.julia/registries/General`
Resolving package versions...
Updating `~/.julia/environments/v1.5/Project.toml`
[d330b81b] ↑ PyPlot v2.8.2 ⇒ v2.9.0
Updating `~/.julia/environments/v1.5/Manifest.toml`
[d330b81b] ↑ PyPlot v2.8.2 ⇒ v2.9.0

julia> using PyPlot
[ Info: Precompiling PyPlot [d330b81b-6aea-500a-939a-2ce795aea3ee]
ERROR: LoadError: syntax: extra token "Base" after end of expression
Stacktrace:
[1] top-level scope at /home/pharaldsson_sym/.julia/packages/PyPlot/XHEG0/src/PyPlot.jl:2
[2] include(::Function, ::Module, ::String) at ./Base.jl:380
[3] include(::Module, ::String) at ./Base.jl:368
[4] top-level scope at none:2
[5] eval at ./boot.jl:331 [inlined]
[6] eval(::Expr) at ./client.jl:467
[7] top-level scope at ./none:3
in expression starting at /home/pharaldsson_sym/.julia/packages/PyPlot/XHEG0/src/PyPlot.jl:2
ERROR: Failed to precompile PyPlot [d330b81b-6aea-500a-939a-2ce795aea3ee] to /home/pharaldsson_sym/.julia/compiled/v1.5/PyPlot/oatAj_ZZkGX.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
```

Reproduce the failure with Julia 1.5.1 using PyPlot v2.9.0, then inspect src/PyPlot.jl at line 2 and the Project file while comparing it with v2.8.2. Done means using PyPlot precompiles successfully without the reported "extra token Base" syntax error.

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