Plots overwrite each other in IJulia

When using IJulia and plotting with Plotly as backend to plots, plots after the first one seem to overwrite the first plot rather than creating a new plot. Example
```julia
# Cell 1
plot(randn())
# Output a nice plot

# cell 2
plot(randn(10))
# no output, plot after cell 1 overwritten instead
```

Versioninfo
Julia v1.3.0
Plotly v0.3.0

