Fix typos (#48)

Author: kianmeng

lib/spandex_datadog/api_server.ex

@@ -222,7 +222,7 @@ defmodule SpandexDatadog.ApiServer do
         end)
       else
         # We get benefits from running in a separate process (like better GC)
-        # So we async/await here to mimic the behavour above but still apply backpressure
+        # So we async/await here to mimic the behaviour above but still apply backpressure
         task = Task.async(fn -> send_and_log(traces, state) end)
         Task.await(task)
       end

test/adapter_test.exs

@@ -65,7 +65,7 @@ defmodule SpandexDatadog.Test.AdapterTest do
     assert(Util.find_span("error_one_deep/0").error == 1)
   end
 
-  test "successul sibling spans are not marked as failures when sibling fails" do
+  test "successful sibling spans are not marked as failures when sibling fails" do
     Util.can_fail(fn -> TracedModule.two_fail_one_succeeds() end)
 
     assert(Util.find_span("error_one_deep/0", 0).error == 1)