Fixes CI Status (#120)

* Move CI workflow to Ubuntu 20.04

* Add newest elixir and OTP to matrix

* Set oldest OTP + Elixir matrix to match documentation

* Update Mix formatting to elixir 1.15+

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     env:
       MIX_ENV: test
     strategy:
@@ -17,10 +17,13 @@ jobs:
         include:
           - pair:
               elixir: 1.7.4
-              otp: 19.3.6.13
+              otp: 22.3.4
           - pair:
               elixir: 1.14.2
-              otp: 24.3
+              otp: 24.3.4.1
+          - pair:
+              elixir: 1.15.0
+              otp: 26.0.1
             lint: lint
     steps:
       - uses: actions/checkout@v2

lib/flow.ex

@@ -1579,7 +1579,7 @@ defmodule Flow do
        {"x", 1}]
 
   """
-  @spec reduce(t, (() -> acc), (term, acc -> acc)) :: t when acc: term()
+  @spec reduce(t, (-> acc), (term, acc -> acc)) :: t when acc: term()
   def reduce(flow, acc_fun, reducer_fun) when is_function(reducer_fun, 2) do
     cond do
       has_any_reduce?(flow) ->
@@ -1627,7 +1627,7 @@ defmodule Flow do
       [[1], [1, 2], [1, 2, 3], [2, 3, 4], [3, 4, 5]]
 
   """
-  @spec emit_and_reduce(t, (() -> acc), (term, acc -> {[event], acc})) :: t
+  @spec emit_and_reduce(t, (-> acc), (term, acc -> {[event], acc})) :: t
         when acc: term(), event: term()
   def emit_and_reduce(flow, acc_fun, reducer_fun) when is_function(reducer_fun, 2) do
     cond do

lib/flow/window.ex

@@ -441,7 +441,7 @@ defmodule Flow.Window do
   We recommend looking at the implementation of `trigger_every/2` as
   an example of a custom trigger.
   """
-  @spec trigger(t, (() -> acc), trigger_fun) :: t
+  @spec trigger(t, (-> acc), trigger_fun) :: t
         when trigger_fun: ([event], acc -> trigger_fun_return),
              trigger_fun_return: cont_tuple | cont_tuple_with_emitted_events | trigger_tuple,
              cont_tuple: {:cont, acc},