randomTensor error and range issues
This may be a stdlib issue, but there's something odd going on. I can't get negative values from randomTensor[float32](shape, -1.0..1.0):

```Nim
import arraymancer
import random

randomize(42)

echo rand(-1.0..1.0)
# without this line, get error from stdlib rand
#echo rand(-1.0..1.0)

# Error: unhandled exception: value out of range: -0.8256829380989075 notin 0.0 .. inf [RangeDefect]
var r = randomTensor[float32]([100, 1], rand(-1.0..1.0))
# with the 2nd echo above uncommented, we get no values out of 100 below zero
echo r
```