Nim devel, cant echo tensor
**Cant `echo` nor `debugEcho` a tensor:**

```nim
$ cat hello_tensor.nim                                                       
import arraymancer

let mytensor = [
    [1, 2, 3], # 0
    [4, 5, 6], # 1
    #0  1  2
  ].toTensor

echo mytensor

$ nim c -r hello_tensor.nim                                                                  

hello_tensor.nim(16, 6) template/generic instantiation of `$` from here
/home/juan/.nimble/pkgs/arraymancer-0.5.0/tensor/display.nim(25, 27) template/generic instantiation of `disp3d` from here
/home/juan/.nimble/pkgs/arraymancer-0.5.0/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)

$ nim --version
Nim Compiler Version 0.19.9 [Linux: amd64]
Compiled at 2019-05-25
Copyright (c) 2006-2019 by Andreas Rumpf
active boot switches: -d:release

$ choosenim stable                                                                           
   Switched to Nim 0.19.6

$ nim c -r hello_tensor.nim                                                                  
Tensor[system.int] of shape [2, 3] of type "int" on backend "Cpu"
|1      2       3|
|4      5       6|

$
```