fix doc test for count function to use f32 type

If the scalar constant is of type f64, tests are failing on devices
that doesn't support double data types. This is a temporary fix.

Author: pradeep

src/algorithm/mod.rs

@@ -242,7 +242,8 @@ dim_reduce_func_def!("
     ```rust
     use arrayfire::{Dim4, gt, print, randu, count};
     let dims = Dim4::new(&[5, 3, 1, 1]);
-    let a = gt(&randu::<f32>(dims), &0.5, false);
+    let cnst: f32 = 0.5;
+    let a = gt(&randu::<f32>(dims), &cnst, false);
     print(&a);
     let b = count(&a, 0);
     print(&b);