`outer` keyword triggers a warning

Creating a cell with the content
```julia
function f()
i = 0
for outer i = 1:3
# empty
end
return i
end
```
results in a warning in the REPL running Pluto
```
┌ Warning: unknown use of `=`. Assignee is unrecognised.
│ ex = :($(Expr(:outer, :i)))
└ @ ExpressionExplorer C:\Users\...\.julia\packages\ExpressionExplorer\ySMFM\src\explore.jl:177
```

The example was taken directly from the Julia manual https://docs.julialang.org/en/v1/base/base/#outer

Tested with ExpressionExplorer 1.1.2.