Doesn't seem to handle Bool negation well

Hi, just trying `@avx` for the first time on a simple loop that includes the negation of a boolean:
```
julia> xs = rand(10)

julia> function foo(x)
count = 0
@avx for i in eachindex(x)
count += !isnan(x[i])
end
count
end
foo (generic function with 1 method)

julia> foo(xs)
ERROR: MethodError: no method matching !(::UInt8)
Closest candidates are:
!(::Missing) at missing.jl:100
!(::Bool) at bool.jl:35
!(::Function) at operators.jl:880
...

```
Is that expected?