SG-29417 [Python API Documentation] Update Python version requirements (#277)

* Remove python 2.7 from readme and docs sections "Minimum requirements"
* Remove references to old Shotgun Server versions.

Author: 000paradox000

README.md

@@ -12,8 +12,7 @@ The latest version can always be found at http://github.com/shotgunsoftware/pyth
 
 ## Minimum Requirements
 
-* ShotGrid server v2.4.12+.
-* Python v2.7 or v3.7
+* Python v3.7
 
 ## Documentation
 Tutorials and detailed documentation about the Python API are available at http://developer.shotgridsoftware.com/python-api).

docs/installation.rst

@@ -6,10 +6,7 @@ Installation
 Minimum Requirements
 ********************
 
-- ShotGrid server v5.4.14 or higher for API v3.0.16+.
-- ShotGrid server v2.4.12 or higher for API v3.0.8.
-- ShotGrid server v1.8 or higher for API v3.0.7.
-- Python 2.7 or Python 3.7
+- Python 3.7
 
 .. note::
     Some features of the API are only supported by more recent versions of the ShotGrid server.