Wait for Process IDs to terminate after killing them

This prevents zombie (defunct) processes on *nix systems. The waitpid()
function throws a ChildProcessError on Windows, so that is handled
accordingly.

undetected_chromedriver/__init__.py

@@ -751,8 +751,9 @@ class Chrome(selenium.webdriver.chrome.webdriver.WebDriver):
     def quit(self):
         try:
             self.service.process.kill()
+            os.waitpid(self.service.process.pid, 0)
             logger.debug("webdriver process ended")
-        except (AttributeError, RuntimeError, OSError):
+        except (AttributeError, ChildProcessError, RuntimeError, OSError):
             pass
         try:
             self.reactor.event.set()
@@ -761,6 +762,7 @@ class Chrome(selenium.webdriver.chrome.webdriver.WebDriver):
             pass
         try:
             os.kill(self.browser_pid, 15)
+            os.waitpid(self.browser_pid, 0)
             logger.debug("gracefully closed browser")
         except Exception as e:  # noqa
             pass
@@ -840,6 +842,12 @@ class Chrome(selenium.webdriver.chrome.webdriver.WebDriver):
         ):
             self.service.process.kill()
 
+            try:
+                # Prevent zombie processes
+                os.waitpid(self.service.process.pid, 0)
+            except ChildProcessError:
+                pass
+
 
 def find_chrome_executable():
     """