Synchronisation parameter declaration error for WebotsNode on ROS 2 Foxy & Eloquent
**Describe the Bug**
Using ROS 2 Foxy (master), any `WebotsNode` crashes on `__init__` when trying to declare `synchronisation` parameter.

**Steps to Reproduce**
1. Use ROS 2 foxy (master) built from source
2. Build webots_ros2 from master
3. Run any example/demo code using `WebotsNode` base node from `webots_ros2_core`

**Expected behavior**
Parameter `synchronisation` must be declared successfully

**Affected Packages**
List of affected packages:
  - webots_ros2_core

**Stracktrace**
```
Traceback (most recent call last):
  File "/home/user/ros/ros/install/test_package/lib/test_package/test_controller", line 11, in <module>
    load_entry_point('test_package', 'console_scripts', 'test_controller')()
  File "/home/user/ros/ros/build/test_package/test_package/test_controller.py", line 36, in main
    test_controller = TestController(args=args)
  File "/home/user/ros/ros/build/test_package/test_package/test_controller.py", line 21, in __init__
    super().__init__('test_controller', args)
  File "/home/user/ros_ws/build/webots_ros2_core/webots_ros2_core/webots_node.py", line 44, in __init__
    self.declare_parameter('synchronization',
  File "/home/user/ros2_foxy/install/rclpy/lib/python3.8/site-packages/rclpy/node.py", line 343, in declare_parameter
    return self.declare_parameters('', [(name, value, descriptor)], ignore_override)[0]
  File "/home/user/ros2_foxy/install/rclpy/lib/python3.8/site-packages/rclpy/node.py", line 438, in declare_parameters
    parameter_list.append(Parameter(name, value=value))
  File "/home/user/ros2_foxy/install/rclpy/lib/python3.8/site-packages/rclpy/parameter.py", line 127, in __init__
    type_ = Parameter.Type.from_parameter_value(value)
  File "/home/user/ros2_foxy/install/rclpy/lib/python3.8/site-packages/rclpy/parameter.py", line 70, in from_parameter_value
    raise TypeError('The given value is not one of the allowed types.')
TypeError: The given value is not one of the allowed types.
```

**System**
 - Webots Version: R2020a revision 1
 - ROS Version: Foxy (master)
 - Operating System: Ubuntu Focal Fossa (20.04LTS) / macOS 10.15.4
 - Graphics Card: N/A
 - Python : Python 3.8.2

**Additional context**
Parameter declaration is no longer compatible with ros foxy

https://github.com/cyberbotics/webots_ros2/blob/a2251d475e45f83be99ba803a531ce8425d25e80/webots_ros2_core/webots_ros2_core/webots_node.py#L44-L45

The following line is effective
```python
self.declare_parameter('synchronization', False)
```

diff --git a/webots_ros2_core/webots_ros2_core/webots_node.py b/webots_ros2_core/webots_ros2_core/webots_node.py
index 42758a7..2d2988a 100644
--- a/webots_ros2_core/webots_ros2_core/webots_node.py
+++ b/webots_ros2_core/webots_ros2_core/webots_node.py
@@ -27,7 +27,6 @@ from webots_ros2_msgs.srv import SetInt
 from rosgraph_msgs.msg import Clock
 
 from rclpy.node import Node
-from rclpy.parameter import Parameter
 
 try:
     append_webots_python_lib_to_path()
@@ -41,8 +40,7 @@ class WebotsNode(Node):
 
     def __init__(self, name, args=None):
         super().__init__(name)
-        self.declare_parameter('synchronization',
-                               Parameter('synchronization', Parameter.Type.BOOL, False))
+        self.declare_parameter('synchronization', False)
         parser = argparse.ArgumentParser()
         parser.add_argument('--webots-robot-name', dest='webotsRobotName', default='',
                             help='Specifies the "name" field of the robot in Webots.')
['webots_ros2_core/webots_ros2_core/webots_node.py']