getheaders() returns uppercase headers in python3 and lowercase in python2

[gene1wood]

The case of the headers returned differs between Python2 and Python3. This may be due to differences between http.client and httplib

Python 2

$ python
Python 2.7.15+ (default, Jul  9 2019, 16:51:35) 
[GCC 7.4.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from agithub.GitHub import GitHub
>>> g = GitHub()
>>> status, data = g.users.octocat.get()
>>> print([x[0] for x in g.getheaders()])
['content-length', 'vary', 'x-xss-protection', 'x-content-type-options', 'etag', 'cache-control', 'referrer-policy', 'status', 'x-ratelimit-remaining', 'x-github-media-type', 'access-control-expose-headers', 'x-github-request-id', 'last-modified', 'date', 'access-control-allow-origin', 'content-security-policy', 'strict-transport-security', 'server', 'x-ratelimit-limit', 'x-frame-options', 'content-type', 'x-ratelimit-reset']

Python 3

$ python3
Python 3.6.8 (default, Aug 20 2019, 17:12:48) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from agithub.GitHub import GitHub
>>> g = GitHub()
>>> status, data = g.users.octocat.get()
>>> print([x[0] for x in g.getheaders()])
['Date', 'Content-Type', 'Content-Length', 'Server', 'Status', 'X-RateLimit-Limit', 'X-RateLimit-Remaining', 'X-RateLimit-Reset', 'Cache-Control', 'Vary', 'ETag', 'Last-Modified', 'X-GitHub-Media-Type', 'Access-Control-Expose-Headers', 'Access-Control-Allow-Origin', 'Strict-Transport-Security', 'X-Frame-Options', 'X-Content-Type-Options', 'X-XSS-Protection', 'Referrer-Policy', 'Content-Security-Policy', 'Vary', 'X-GitHub-Request-Id']