BoundsError: attempt to access 199-element Vector{Float64} at index [1:200]

**Describe the bug**
In OnlineStats.jl there is an example about HeatMap which throws an error when I activate plotlyjs

```
using OnlineStats
using Plots
plotlyjs() # without ploytljs(), e.g. without anything, or with gr() everything works

xy = zip(randn(10^6), randn(10^6))
o = fit!(HeatMap(-5:.1:5, -5:.1:5), xy)
plot(o)

xy = zip(1 .+ randn(10^6) ./ 10, randn(10^6))
o = HeatMap(xy)
plot(o, marginals=false)
plot(o)
```

it throws
```
BoundsError: attempt to access 199-element Vector{Float64} at index [1:200]

Stacktrace:
[1] throw_boundserror(A::Vector{Float64}, I::Tuple{UnitRange{Int64}})
@ Base ./abstractarray.jl:651
[2] checkbounds
@ ./abstractarray.jl:616 [inlined]
[3] getindex(A::Vector{Float64}, I::UnitRange{Int64})
@ Base ./array.jl:807
[4] plotly_series_segments(series::Plots.Series, plotattributes_base::Dict{Symbol, Any}, x::StepRangeLen{Float64, Base.TwicePrecision{Float64}, Base.TwicePrecision{Float64}}, y::Vector{Float64}, z::Nothing, clims::Tuple{Float64, Float64})
@ Plots ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:873
[5] plotly_series(plt::Plots.Plot{Plots.PlotlyBackend}, series::Plots.Series)
@ Plots ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:606
[6] #387
@ ./array.jl:0 [inlined]
[7] MappingRF
@ ./reduce.jl:93 [inlined]
[8] _foldl_impl(op::Base.MappingRF{Plots.var"#387#388"{Plots.Plot{Plots.PlotlyBackend}}, Base.BottomRF{typeof(vcat)}}, init::Base._InitialValue, itr::Vector{Plots.Series})
@ Base ./reduce.jl:62
[9] foldl_impl
@ ./reduce.jl:48 [inlined]
[10] mapfoldl_impl
@ ./reduce.jl:44 [inlined]
[11] #mapfoldl#214
@ ./reduce.jl:160 [inlined]
[12] mapfoldl
@ ./reduce.jl:160 [inlined]
[13] #mapreduce#218
@ ./reduce.jl:287 [inlined]
[14] mapreduce
@ ./reduce.jl:287 [inlined]
[15] #reduce#220
@ ./reduce.jl:456 [inlined]
[16] reduce
@ ./reduce.jl:456 [inlined]
[17] plotly_series
@ ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:1034 [inlined]
[18] plotly_series_json(plt::Plots.Plot{Plots.PlotlyBackend})
@ Plots ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:1038
[19] js_body
@ ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:1103 [inlined]
[20] plotly_html_body(plt::Plots.Plot{Plots.PlotlyBackend}, style::Nothing)
@ Plots ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:1091
[21] plotly_html_body
@ ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:1065 [inlined]
[22] html_body
@ ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:1043 [inlined]
[23] embeddable_html
@ ~/.julia/packages/Plots/qbc7U/src/backends/web.jl:26 [inlined]
[24] _show(io::IOBuffer, #unused#::MIME{Symbol("text/html")}, plt::Plots.Plot{Plots.PlotlyBackend})
@ Plots ~/.julia/packages/Plots/qbc7U/src/backends/plotly.jl:1123
[25] show(io::IOBuffer, m::MIME{Symbol("text/html")}, plt::Plots.Plot{Plots.PlotlyBackend})
@ Plots ~/.julia/packages/Plots/qbc7U/src/output.jl:213
[26] sprint(::Function, ::MIME{Symbol("text/html")}, ::Vararg{Any, N} where N; context::Nothing, sizehint::Int64)
@ Base ./strings/io.jl:105
[27] sprint
@ ./strings/io.jl:101 [inlined]
[28] _ijulia_display_dict(plt::Plots.Plot{Plots.PlotlyBackend})
@ Plots ~/.julia/packages/Plots/qbc7U/src/ijulia.jl:50
[29] display_dict(plt::Plots.Plot{Plots.PlotlyBackend})
@ Plots ~/.julia/packages/Plots/qbc7U/src/init.jl:93
[30] #invokelatest#2
@ ./essentials.jl:708 [inlined]
[31] invokelatest
@ ./essentials.jl:706 [inlined]
[32] execute_request(socket::ZMQ.Socket, msg::IJulia.Msg)
@ IJulia ~/.julia/packages/IJulia/e8kqU/src/execute_request.jl:112
[33] #invokelatest#2
@ ./essentials.jl:708 [inlined]
[34] invokelatest
@ ./essentials.jl:706 [inlined]
[35] eventloop(socket::ZMQ.Socket)
@ IJulia ~/.julia/packages/IJulia/e8kqU/src/eventloop.jl:8
[36] (::IJulia.var"#15#18")()
@ IJulia ./task.jl:411
```

**Version info**

Please provide the following:

1. output of julia command `versioninfo()`
```
julia> versioninfo()
Julia Version 1.6.1
Commit 6aaedecc44 (2021-04-23 05:59 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: Intel(R) Core(TM) i7-1065G7 CPU @ 1.30GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-11.0.1 (ORCJIT, icelake-client)
```

2. Output running the following in Julia 0.7 or greater: `using Pkg; pkg"status"` (if you are on Julia 0.6 or earlier run `Pkg.status()`)
```
julia> using Pkg; pkg"status"
Status `~/.julia/environments/v1.6/Project.toml`
[a15396b6] OnlineStats v1.5.13
[925886fa] OnlineStatsBase v1.4.9
[f0f68f2c] PlotlyJS v0.18.8
[91a5bcdd] Plots v1.25.0
...
```