chore: fix runtime warnings

Author: Krapaince

lib/mimemail.ex

@@ -53,7 +53,8 @@ defmodule MimeMail do
         escaped_bound = Regex.escape(bound)
         body 
           |> String.split(~r"\s*--#{escaped_bound}\s*") 
-          |> Enum.slice(1..-2//-1) 
+          |> Enum.drop(1)
+          |> Enum.drop(-1)
           |> Enum.map(&from_string/1) 
           |> Enum.map(&decode_body/1)
       {"text/"<>_,%{charset: charset}} ->

lib/spf.ex

@@ -289,7 +289,13 @@ defmodule SPF do
     delimiters = for <<c<-delimiters>>, c in [?.,?-,?+,?,,?/,?_,?=], into: "", do: <<c>>
     components=String.split(expanded,Regex.compile!("["<>delimiters<>"]"))
     components=if reversed?, do: Enum.reverse(components), else: components
-    components=Enum.slice(components,max(-length(components),start_index)..-1)
+    len = length(components)
+    components =
+      cond do
+        start_index == 0 -> components
+        len <= -start_index -> components
+        true -> Enum.drop(components, len + start_index)
+      end
     Enum.join(components,".")
   end
 end