Merge pull request #3000 from canyon289/contributing_typo

Fix minor typos in CONTRIBUTING.md

Author: fonnesbeck

CONTRIBUTING.md

@@ -11,7 +11,7 @@ There are 4 main ways of contributing to the PyMC3 project (in descending order
 
 # Opening issues
 
-We appreciate being notified of problems with the existing PyMC code. We prefer that issues be filed the on [Gitub Issue Tracker](https://github.com/pymc-devs/pymc3/issues), rather than on social media or by direct email to the developers.
+We appreciate being notified of problems with the existing PyMC code. We prefer that issues be filed the on [Github Issue Tracker](https://github.com/pymc-devs/pymc3/issues), rather than on social media or by direct email to the developers.
 
 Please verify that your issue is not being currently addressed by other issues or pull requests by using the GitHub search tool to look for key words in the project issue tracker.
 
@@ -21,7 +21,7 @@ While issue reporting is valuable, we strongly encourage users who are inclined
 
 Contributors are also encouraged to contribute new code to enhance PyMC3's functionality, also via pull requests. Please consult the [PyMC3 documentation](https://pymc-devs.github.io/pymc3/) to ensure that any new contribution does not strongly overlap with existing functionality.
 
-The preferred workflow for contributing to PyMC3 is to fork the [GitHUb repository](https://github.com/pymc-devs/pymc3/), clone it to your local machine, and develop on a feature branch.
+The preferred workflow for contributing to PyMC3 is to fork the [GitHub repository](https://github.com/pymc-devs/pymc3/), clone it to your local machine, and develop on a feature branch.
 
 ## Steps:
 
@@ -145,8 +145,8 @@ $  . ./scripts/test.sh # takes a while!
 This should be quite close to how the tests run on TravisCI.
 
 If the container was started without opening the browser, you
-need the a token to work with the notebook. This token can be
-access with
+need the notebook instances token to work with the notebook. This token can be
+accessed with
 
 ```
 docker exec -it pymc3 jupyter notebook list