didnt -> didn't

Author: ss18

testing/test_mark.py

@@ -435,7 +435,7 @@ class TestA(object):
                 def test_b(self):
                     assert True
                 class TestC(object):
-                    # this one didnt get marked
+                    # this one didn't get marked
                     def test_d(self):
                         assert True
         """

testing/test_nose.py

@@ -253,7 +253,7 @@ def test_fun(self):
 
 
 def test_setup_teardown_linking_issue265(testdir):
-    # we accidentally didnt integrate nose setupstate with normal setupstate
+    # we accidentally didn't integrate nose setupstate with normal setupstate
     # this test ensures that won't happen again
     testdir.makepyfile(
         '''