Error: type mismatch on echo
Hi !

I'm a newbie with nim and I was trying out some arraymancer examples to get a feel on the usage, but when I run the example code

```
import arraymancer

let d = [[1, 2, 3], [4, 5, 6]].toTensor()

echo d
# Tensor of shape 2x3 of type "int" on backend "Cpu"
# |1      2       3|
# |4      5       6|

echo d.rank # 2
echo d.shape # @[2, 3]
echo d.strides # @[3, 1] => Next row is 3 elements away in memory while next column is 1 element away.
echo d.offset # 0
```


compilation fails:
> bla.nim(5, 6) template/generic instantiation of `$` from here
> ../../.nimble/pkgs/arraymancer-#head/tensor/display.nim(25, 27) template/generic instantiation of `disp3d` from here
> ../../.nimble/pkgs/arraymancer-#head/tensor/private/p_display.nim(96, 17) Error: type mismatch: got <Tensor[system.int], proc (x: GenericParam): untyped>
> but expected one of: 
> proc map[T, S](s: openArray[T]; op: proc (x: T): S {.closure.}): seq[S]
>   first type mismatch at position: 1
>   required type: openarray[T]
>   but expression 't0' is of type: Tensor[system.int]
> 
> expression: map(t0, proc (x: auto): auto = $x)
> [Finished in 1.2s with exit code 1]

if I remove `echo d` it compiles and runs fine.
I'm running latest nim from git (1:0.19.4.r1306.c7c495f08-1) and have the issue on arraymancer 5.0 and head.
Any help is appreciated!
cheers
Simon


