Make "s" in "https" optional to match URL w/ regex

Some folks may be using a GitHub Enterprise server that doesn't support
HTTPS.

github3/github.py

@@ -1000,7 +1000,7 @@ class GitHub(GitHubCore):
         :returns: bool
         """
         from re import match
-        m = match('https://[\w\d\-\.\:]+/\w+/[\w\._-]+/events/\w+', topic)
+        m = match('https?://[\w\d\-\.\:]+/\w+/[\w\._-]+/events/\w+', topic)
         status = False
         if mode and topic and callback and m:
             data = [('hub.mode', mode), ('hub.topic', topic),

github3/issues/issue.py

@@ -77,7 +77,7 @@ class Issue(GitHubCore):
         self.number = issue.get('number')
         #: Dictionary URLs for the pull request (if they exist)
         self.pull_request = issue.get('pull_request')
-        m = match('https://[\w\d\-\.\:]+/(\S+)/(\S+)/(?:issues|pull)/\d+',
+        m = match('https?://[\w\d\-\.\:]+/(\S+)/(\S+)/(?:issues|pull)/\d+',
                   self.html_url)
         #: Returns ('owner', 'repository') this issue was filed on.
         self.repository = m.groups()

github3/pulls.py

@@ -183,7 +183,7 @@ class PullRequest(GitHubCore):
         #: GitHub.com url for review comments (not a template)
         self.review_comments_url = pull.get('review_comments_url')
-        m = match('https://[\w\d\-\.\:]+/(\S+)/(\S+)/(?:issues|pull)?/\d+',
+        m = match('https?://[\w\d\-\.\:]+/(\S+)/(\S+)/(?:issues|pull)?/\d+',
                   self.issue_url)
         #: Returns ('owner', 'repository') this issue was filed on.
         self.repository = m.groups()