Make Chromedriver escript Compatible

[alecho]

Issue

Similar to #192 but for chromedriver. When embedding Wallaby in an escript Wallaby.Experimental.Chrome.Chromedriver fails to start.

00:13:35.372 [info]  Application wallaby exited: Wallaby.start(:normal, []) returned an error: shutdown: failed to start child: Wallaby.Experimental.Chrome
    ** (EXIT) shutdown: failed to start child: Wallaby.Experimental.Chrome.Chromedriver
        ** (EXIT) an exception was raised:
            ** (ArgumentError) unknown application: :wallaby
                (elixir) lib/application.ex:699: Application.app_dir/1
                (wallaby) lib/wallaby/experimental/chrome/chromedriver.ex:50: Wallaby.Experimental.Chrome.Chromedriver.wrapper_script/0
                (wallaby) lib/wallaby/experimental/chrome/chromedriver.ex:43: Wallaby.Experimental.Chrome.Chromedriver.start_chromedriver/1
                (wallaby) lib/wallaby/experimental/chrome/chromedriver.ex:23: Wallaby.Experimental.Chrome.Chromedriver.init/1
                (stdlib) gen_server.erl:374: :gen_server.init_it/2
                (stdlib) gen_server.erl:342: :gen_server.init_it/6
                (stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3

This is because we can't access files within priv in escripts. The fix is similar to #193 where we load the script as a module attribute at compilation.