Merge pull request #165 from janrope/fix_colab

#minor [bug fix] Google colab ray version and link in readme

README.md

@@ -21,7 +21,7 @@
 [![Documentation Status](https://readthedocs.org/projects/marllib/badge/?version=latest)](https://marllib.readthedocs.io/en/latest/)
 [![GitHub issues](https://img.shields.io/github/issues/Replicable-MARL/MARLlib)](https://github.com/Replicable-MARL/MARLlib/issues)
 [![PyPI version](https://badge.fury.io/py/marllib.svg)](https://badge.fury.io/py/marllib)
-[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/Replicable-MARL/MARLlib/blob/rllib_1.8.0_dev/marllib.ipynb)
+[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/Replicable-MARL/MARLlib/blob/master/marllib.ipynb)
 [![Organization](https://img.shields.io/badge/Organization-ReLER_RL-blue.svg)](https://github.com/Replicable-MARL/MARLlib)
 [![Organization](https://img.shields.io/badge/Organization-PKU_MARL-blue.svg)](https://github.com/Replicable-MARL/MARLlib)
 [![Awesome](https://awesome.re/badge.svg)](https://marllib.readthedocs.io/en/latest/resources/awesome.html)
@@ -359,7 +359,7 @@ MARLlib provides some practical examples for you to refer to.
 ## Tutorials
 
 Try MPE + MAPPO examples on Google Colaboratory!
-[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/Replicable-MARL/MARLlib/blob/rllib_1.8.0_dev/marllib.ipynb)
+[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/Replicable-MARL/MARLlib/blob/master/marllib.ipynb)
 More tutorial documentations are available [here](https://marllib.readthedocs.io/).
 
 ## Awesome List

marllib.ipynb

@@ -50,7 +50,7 @@
    },
    "outputs": [],
    "source": [
-    "!/usr/local/bin/pip install protobuf==3.20.0 marllib==1.0.3 ray[rllib] gym==0.22.0"
+    "!/usr/local/bin/pip install protobuf==3.20.0 marllib==1.0.3 ray[rllib]==1.8.0 gym==0.22.0"
    ]
   },
   {