When attempting to plot a histogram of `DateTime`

I get the following error

```
ERROR: LoadError: InexactError()
Stacktrace:
[1] convert(::Type{Int64}, ::Float64) at ./float.jl:679
[2] UTM at ./dates/types.jl:74 [inlined]
[3] datetimeformatter(::Float64) at /home/expandingman/.julia/v0.6/Plots/src/recipes.jl:982
[4] collect_to!(::Array{String,1}, ::Base.Generator{Array{Float64,1},Plots.#datetimeformatter}, ::Int64, ::Int64) at ./array.jl:474
[5] _collect(::Array{Float64,1}, ::Base.Generator{Array{Float64,1},Plots.#datetimeformatter}, ::Base.EltypeUnknown, ::Base.HasShape) at ./array.jl:455
[6] map(::Function, ::Array{Float64,1}) at ./abstractarray.jl:1865
[7] optimal_ticks_and_labels(::Plots.Axis, ::Void) at /home/expandingman/.julia/v0.6/Plots/src/axes.jl:220
[8] get_ticks(::Plots.Axis) at /home/expandingman/.julia/v0.6/Plots/src/axes.jl:243
[9] _before_layout_calcs(::Plots.Plot{Plots.PyPlotBackend}) at /home/expandingman/.julia/v0.6/Plots/src/backends/pyplot.jl:1053
[10] prepare_output(::Plots.Plot{Plots.PyPlotBackend}) at /home/expandingman/.julia/v0.6/Plots/src/plot.jl:251
[11] show(::IOStream, ::MIME{Symbol("image/png")}, ::Plots.Plot{Plots.PyPlotBackend}) at /home/expandingman/.julia/v0.6/Plots/src/output.jl:207
[12] png(::Plots.Plot{Plots.PyPlotBackend}, ::String) at /home/expandingman/.julia/v0.6/Plots/src/output.jl:8
[13] savefig(::Plots.Plot{Plots.PyPlotBackend}, ::String) at /home/expandingman/.julia/v0.6/Plots/src/output.jl:123
[14] include_from_node1(::String) at ./loading.jl:569
[15] include(::String) at ./sysimg.jl:14
while loading /home/expandingman/AuditProject/testplots0.jl, in expression starting on line 14
```