Change main install docs

docs/Installation-Anaconda-Windows.md

 connected to the Internet and then type in the Anaconda Prompt:
 
 ```console
-python -m pip install mlagents==0.26.0.dev0
+python -m pip install mlagents==0.25.0
 ```
 
 This will complete the installation of all the required Python packages to run
 this, you can try:
 
 ```console
-python -m pip install mlagents==0.26.0.dev0 --no-cache-dir
+python -m pip install mlagents==0.25.0 --no-cache-dir
 ```
 
 This `--no-cache-dir` tells the pip to disable the cache.

docs/Installation.md

 run from the command line:
 
 ```sh
-python -m pip install mlagents==0.26.0.dev0
+python -m pip install mlagents==0.25.0
 ```
 
 Note that this will install `mlagents` from PyPi, _not_ from the cloned

docs/Training-on-Microsoft-Azure.md

    instance, and set it as the working directory.
 2. Install the required packages:
    Torch: `pip3 install torch==1.7.0 -f https://download.pytorch.org/whl/torch_stable.html` and
-   MLAgents: `python -m pip install mlagents==0.26.0.dev0`
+   MLAgents: `python -m pip install mlagents==0.25.0`
 
 ## Testing
 

ml-agents-envs/README.md

 Install the `mlagents_envs` package with:
 
 ```sh
-python -m pip install mlagents_envs==0.26.0.dev0
+python -m pip install mlagents_envs==0.25.0
 ```
 
 ## Usage & More Information

ml-agents/README.md

 Install the `mlagents` package with:
 
 ```sh
-python -m pip install mlagents==0.26.0.dev0
+python -m pip install mlagents==0.25.0
 ```
 
 ## Usage & More Information