Fix dialyzer test when running locally (#271)

* Fix dialyzer test when running locally

I'm testing running locally on arch linux. It appear that for me locally
for the "reports diagnostics then clears them once problems are fixed"
test I get the output I get the message:

    [ElixirLS Dialyzer] Analyzing 3 modules: [A, B, :erlang]

Instead of:

    [ElixirLS Dialyzer] Analyzing 2 modules: [A, B]

Adding a function definition in module C causes :erlang to not be
detected as needing to be analyzed.

* :lib.flush_receive() doesn't exist in the same place on supported erlang versions

DEVELOPMENT.md

@@ -11,3 +11,9 @@ Push the tag
 - `cd release`
 - `zip elixir-ls.zip *`
 - Attach elixir-ls.zip to the release on github https://github.com/elixir-lsp/elixir-ls/releases
+
+# Debugging
+
+If you're debugging a running server than `IO.inspect` is a good approach, any messages you create with it will be sent to your LSP client as a log message
+
+To debug in tests you can use `IO.inspect(Process.whereis(:user), message, label: "message")` to send your output directly to the group leader of the test process.

apps/language_server/test/fixtures/dialyzer/lib/c.ex

@@ -1,2 +1,5 @@
 defmodule C do
+  def myfun do
+    1
+  end
 end