Simplify version matching code

This slightly modifies the semantics for the sake of replacing a
slightly non-obvious function with a call to Version.match?/3. It also
fixes a credo warning about Enum.filter that would have added a couple
lines of code to fix.

The end result is that if you're on a prerelease, you'll get notified to
upgrade to a later prerelease even if it's not the same major, minor,
patch version. This seems like a highly unlikely use case given our
history of releases with this project.

.dialyzer_ignore.exs

@@ -1,5 +1,5 @@
 # Run `mix dialyzer --format short` for strings
 [
-  {"lib/nerves_bootstrap/update_checker.ex:7:9:unknown_function Function Hex.start/0 does not exist."},
-  {"lib/nerves_bootstrap/update_checker.ex:8:45:unknown_function Function Hex.API.Package.get/2 does not exist."}
+  {"lib/nerves_bootstrap/update_checker.ex:9:9:unknown_function Function Hex.start/0 does not exist."},
+  {"lib/nerves_bootstrap/update_checker.ex:10:45:unknown_function Function Hex.API.Package.get/2 does not exist."}
 ]

lib/nerves_bootstrap/update_checker.ex

@@ -1,4 +1,6 @@
 defmodule Nerves.Bootstrap.UpdateChecker do
+  @moduledoc false
+
   @doc """
   Check for a nerves_bootstrap release
   """
@@ -30,9 +32,11 @@ defmodule Nerves.Bootstrap.UpdateChecker do
 
   @spec select_update([Version.t()], Version.t()) :: Version.t() | nil
   def select_update(releases, current_version) do
+    req = Version.parse_requirement!("> #{current_version}")
+    allow_pre = current_version.pre != []
+
     releases
-    |> Enum.filter(&(Version.compare(&1, current_version) == :gt))
-    |> Enum.filter(pre_release_filter(current_version))
+    |> Enum.filter(&Version.match?(&1, req, allow_pre: allow_pre))
     |> Enum.sort(&(Version.compare(&1, &2) == :gt))
     |> List.first()
   end
@@ -58,22 +62,4 @@ defmodule Nerves.Bootstrap.UpdateChecker do
       :reset
     ])
   end
-
-  # Return a function that filters releases based on whether the current version is a pre-release
-  defp pre_release_filter(%{pre: []}) do
-    &(Map.get(&1, :pre) == [])
-  end
-
-  defp pre_release_filter(%{major: major, minor: minor, patch: patch}) do
-    fn
-      %{pre: []} ->
-        true
-
-      %{major: ^major, minor: ^minor, patch: ^patch} ->
-        true
-
-      _ ->
-        false
-    end
-  end
 end

test/nerves_bootstrap/update_checker_test.exs

@@ -20,11 +20,10 @@ defmodule UpdateChecker.UpdateCheckerTest do
     current_version = Version.parse!("1.0.0-rc.0")
 
     releases = [
-      "1.1.0-rc.0",
-      "1.0.0-rc.1",
       "0.8.2",
       "1.0.0-rc.0",
-      "0.8.1"
+      "0.8.1",
+      "1.0.0-rc.1"
     ]
 
     releases = Enum.map(releases, &Version.parse!/1)