apply black with py2.7 compat

.github/PULL_REQUEST_TEMPLATE.md

@@ -7,4 +7,4 @@ Delete them if they are not appropriate for this pull request.
 - [ ] I have properly documented new or changed features in the documention or in the docstrings
 - [ ] I have properly documented unusual changes to the code in the comments around it
 - [ ] I have made note of any breaking/backwards incompatible changes
-- [ ] I formatted my code using `black -t py36` 
+- [ ] I formatted my code using `black` 

.github/workflows/ci.yml

@@ -11,4 +11,4 @@ jobs:
       - name: Black Code Formatter
         uses: lgeiger/[email protected]    
         with:
-          args: "--check --target-version py36 $GITHUB_WORKSPACE"
+          args: "--check --target-version py27 $GITHUB_WORKSPACE"

CONTRIBUTING.md

@@ -7,7 +7,7 @@
 - If you introduce a new functionality or fix a subtle bug, document it in the docstring/code.
 - Moviepy's team adopted [black](https://github.com/psf/black) to autoformat the code. This is  enforced for any pull request. 
 
-> Tip: use `black -t py36 .` to autoformat your code, or set black as a plugin of your editor. 
+> Tip: use `black -t py27 .` to autoformat your code, or set black as a plugin of your editor. 
 
 
 ## Using Github