Add 'submitted at' to PullRequestReview (#565)

This field is not currently listed in the Github documentation at
https://developer.github.com/v3/pulls/reviews/, but it's been included
since Github 2.9

(It even exists in the test data returned for the original
PullRequestReview PR)

github/PullRequestReview.py

@@ -95,6 +95,14 @@ class PullRequestReview(github.GithubObject.CompletableGithubObject):
         self._completeIfNotSet(self._pull_request_url)
         return self._pull_request_url.value
 
+    @property
+    def submitted_at(self):
+        """
+        :type: datetime.datetime
+        """
+        self._completeIfNotSet(self._submitted_at)
+        return self._submitted_at.value
+
     def _initAttributes(self):
         self._id = github.GithubObject.NotSet
         self._user = github.GithubObject.NotSet
@@ -103,6 +111,7 @@ class PullRequestReview(github.GithubObject.CompletableGithubObject):
         self._state = github.GithubObject.NotSet
         self._html_url = github.GithubObject.NotSet
         self._pull_request_url = github.GithubObject.NotSet
+        self._submitted_at = github.GithubObject.NotSet
 
     def _useAttributes(self, attributes):
         if "id" in attributes:  # pragma no branch
@@ -119,3 +128,5 @@ class PullRequestReview(github.GithubObject.CompletableGithubObject):
             self._html_url = self._makeStringAttribute(attributes["html_url"])
         if "pull_request_url" in attributes:  # pragma no branch
             self._pull_request_url = self._makeStringAttribute(attributes["pull_request_url"])
+        if "submitted_at" in attributes:  # pragma no branch
+            self._submitted_at = self._makeDatetimeAttribute(attributes["submitted_at"])

github/tests/PullRequestReview.py

@@ -26,6 +26,8 @@
 
 import Framework
 
+import datetime
+
 class PullRequestReview(Framework.TestCase):
     def setUp(self):
         Framework.TestCase.setUp(self)
@@ -46,6 +48,7 @@ class PullRequestReview(Framework.TestCase):
         self.assertEqual(self.pullreview.state, "APPROVED")
         self.assertEqual(self.pullreview.html_url, "https://github.com/PyGithub/PyGithub/pull/538#pullrequestreview-28482091")
         self.assertEqual(self.pullreview.pull_request_url, "https://api.github.com/repos/PyGithub/PyGithub/pulls/538")
+        self.assertEqual(self.pullreview.submitted_at, datetime.datetime(2017, 3, 22, 19, 6, 59))
 
         # test __repr__() based on this attributes
         self.assertEqual(self.pullreview.__repr__(), 'PullRequestReview(user=NamedUser(login="jzelinskie"), id=28482091)')