fix bind_* NIF typespecs (#318)

Author: ademenev

Diff for: lib/exqlite/sqlite3_nif.ex

@@ -72,19 +72,19 @@ defmodule Exqlite.Sqlite3NIF do
   @spec bind_parameter_count(statement) :: integer
   def bind_parameter_count(_stmt), do: :erlang.nif_error(:not_loaded)
 
-  @spec bind_text(statement, non_neg_integer, String.t()) :: :ok
+  @spec bind_text(statement, non_neg_integer, String.t()) :: integer()
   def bind_text(_stmt, _index, _text), do: :erlang.nif_error(:not_loaded)
 
-  @spec bind_blob(statement, non_neg_integer, binary) :: :ok
+  @spec bind_blob(statement, non_neg_integer, binary) :: integer()
   def bind_blob(_stmt, _index, _blob), do: :erlang.nif_error(:not_loaded)
 
-  @spec bind_integer(statement, non_neg_integer, integer) :: :ok
+  @spec bind_integer(statement, non_neg_integer, integer) :: integer()
   def bind_integer(_stmt, _index, _integer), do: :erlang.nif_error(:not_loaded)
 
-  @spec bind_float(statement, non_neg_integer, float) :: :ok
+  @spec bind_float(statement, non_neg_integer, float) :: integer()
   def bind_float(_stmt, _index, _float), do: :erlang.nif_error(:not_loaded)
 
-  @spec bind_null(statement, non_neg_integer) :: :ok
+  @spec bind_null(statement, non_neg_integer) :: integer()
   def bind_null(_stmt, _index), do: :erlang.nif_error(:not_loaded)
 
   @spec reset(statement) :: :ok