webdriver_server: change default binary to geckodriver

geckodriver used to be called wires, but it is now called geckodriver.

wptrunner/webdriver_server.py

@@ -153,7 +153,7 @@ def make_command(self):
 
 
 class GeckoDriverServer(WebDriverServer):
-    def __init__(self, logger, marionette_port=2828, binary="wires",
+    def __init__(self, logger, marionette_port=2828, binary="geckodriver",
                  host="127.0.0.1", port=None):
         env = os.environ.copy()
         env["RUST_BACKTRACE"] = "1"