Fixup compiler warnings

Author: dbernheisel

lib/parser/serial.ex

@@ -97,7 +97,8 @@ defmodule DateTimeParser.Parser.Serial do
     )
   end
 
-  defp time_from_serial(0.0), do: {0, 0, 0}
+  defp time_from_serial(+0.0), do: {0, 0, 0}
+  defp time_from_serial(-0.0), do: {0, 0, 0}
 
   defp time_from_serial(serial_time) do
     {hours, min_fraction} = split_float(serial_time * 24)
@@ -123,7 +124,7 @@ defmodule DateTimeParser.Parser.Serial do
   defp split_float(float) when float < 0 do
     whole = abs(float) |> Float.floor() |> round()
     fraction = 1 - (abs(float) - whole)
-    fraction = if fraction == 1.0, do: 0.0, else: fraction
+    fraction = if fraction == 1.0, do: +0.0, else: fraction
     {whole * -1, fraction}
   end