Why is it not allowed to calculate the dot product of two row vectors?

Example:

```
julia> b=ones(3)'
1×3 RowVector{Float64,Array{Float64,1}}:
1.0 1.0 1.0
julia> a=ones(3)'
1×3 RowVector{Float64,Array{Float64,1}}:
1.0 1.0 1.0
julia> dot(a,b)
ERROR: MethodError: no method matching dot(::RowVector{Float64,Array{Float64,1}}, ::RowVector{Float64,Array{Float64,1}})
julia>
```