Change percentiles type in Measurements to :map

- Currently there is a bug on ecto when parsing fields of type {:map, :float}
with exponential notation. This is a temporary solution to have the benchmarks
results being displayed correctly.

Signed-off-by: Tallys Martins <tallysmartins@gmail.com>

lib/elixir_bench/benchmarks/measurement.ex

@@ -19,7 +19,7 @@ defmodule ElixirBench.Benchmarks.Measurement do
     field :ips, :float
     field :std_dev_ips, :float
 
-    field :percentiles, {:map, :float}
+    field :percentiles, :map
 
     timestamps(type: :utc_datetime)
   end