Fix failing test.

In Selenium 2.53.0, the error code mapper would not match the
UnsupportedCommandException and so would return the default
value of UNHANDLED_ERROR. In 3.0, we correctly map this to
the more appropriate error code of UNKNOWN_COMMAND, which
describes the lack of a match more appropriately.

java/server/test/org/openqa/selenium/remote/server/DriverServletTest.java

@@ -182,7 +182,7 @@ public void handlesInvalidCommandsToRootOfDriverService()
     assertEquals(500, response.getStatus());
 
     JsonObject jsonResponse = new JsonParser().parse(response.getBody()).getAsJsonObject();
-    assertEquals(ErrorCodes.UNHANDLED_ERROR, jsonResponse.get("status").getAsInt());
+    assertEquals(ErrorCodes.UNKNOWN_COMMAND, jsonResponse.get("status").getAsInt());
 
     JsonObject value = jsonResponse.get("value").getAsJsonObject();
     assertTrue(value.get("message").getAsString().startsWith("POST /"));