ndarray: fix type convertion in setindex! (#398)

Make this case work
```julia
x = mx.NDArray([1, 2, 3]);
x[:] = 1.1
```

src/ndarray.jl

@@ -356,7 +356,7 @@ end
 
 function setindex!(arr::NDArray, val::Real, ::Colon)
   @assert arr.writable
-  _set_value(out=arr, src=convert(eltype(arr), val))
+  _set_value(out = arr, src = dump_mx_param(val))
 end
 
 function setindex!(arr::NDArray, val::Array{T}, ::Colon) where T<:Real

test/unittest/ndarray.jl

@@ -157,6 +157,14 @@ function test_linear_idx()
     x[24] = 42
     @test copy(x[24]) == [42]
   end
+
+  info("NDArray::setindex!::type convert")
+  let
+    x = NDArray([1, 2, 3])
+    @test eltype(x) == Int
+    x[:] = π
+    @test copy(x) == [3, 3, 3]
+  end
 end  # function test_linear_idx
 
 function test_first()