Update Git Links (#48)

Author: peifeng-unity

Diff for: .gitmodules

@@ -1,9 +1,9 @@
 [submodule "tutorials/pick_and_place/ROS/src/niryo_one_ros"]
 	path = tutorials/pick_and_place/ROS/src/niryo_one_ros
-	url = git@github.com:NiryoRobotics/niryo_one_ros.git
+	url = https://github.com/NiryoRobotics/niryo_one_ros.git
 [submodule "tutorials/pick_and_place/ROS/src/moveit_msgs"]
 	path = tutorials/pick_and_place/ROS/src/moveit_msgs
-	url = git@github.com:ros-planning/moveit_msgs.git
+	url = https://github.com/ros-planning/moveit_msgs.git
 [submodule "tutorials/pick_and_place/ROS/src/ros_tcp_endpoint"]
 	path = tutorials/pick_and_place/ROS/src/ros_tcp_endpoint
-	url = git@github.com:Unity-Technologies/ROS-TCP-Endpoint.git
+	url = https://github.com/Unity-Technologies/ROS-TCP-Endpoint.git

Diff for: tutorials/pick_and_place/1_urdf.md

@@ -15,7 +15,7 @@ This part includes downloading and installing the Unity Editor, setting up a bas
 ## Setting up the Unity Scene
 1. Clone this repo to a location on your local machine:
     ```bash
-    git clone --recurse-submodules git@github.com:Unity-Technologies/Unity-Robotics-Hub.git
+    git clone --recurse-submodules https://github.com/Unity-Technologies/Unity-Robotics-Hub.git
     ```
 
 1. Install [Unity Hub](https://unity3d.com/get-unity/download).