Fix typos discovered by codespell

tests/integration/test_basic.py

@@ -11,7 +11,7 @@ import vcr
 
 def test_nonexistent_directory(tmpdir, httpbin):
     """If we load a cassette in a nonexistent directory, it can save ok"""
-    # Check to make sure directory doesnt exist
+    # Check to make sure directory doesn't exist
     assert not os.path.exists(str(tmpdir.join("nonexistent")))
 
     # Run VCR to create dir and cassette file

tests/integration/test_register_persister.py

@@ -30,7 +30,7 @@ def test_save_cassette_with_custom_persister(tmpdir, httpbin):
     my_vcr = vcr.VCR()
     my_vcr.register_persister(CustomFilesystemPersister)
 
-    # Check to make sure directory doesnt exist
+    # Check to make sure directory doesn't exist
     assert not os.path.exists(str(tmpdir.join("nonexistent")))
 
     # Run VCR to create dir and cassette file using new save_cassette callback

tests/unit/test_migration.py

@@ -44,4 +44,4 @@ def test_try_migrate_with_invalid_or_new_cassettes(tmpdir):
     for file_path in files:
         shutil.copy(file_path, cassette)
         assert not vcr.migration.try_migrate(cassette)
-        assert filecmp.cmp(cassette, file_path)  # shold not change file
+        assert filecmp.cmp(cassette, file_path)  # should not change file

vcr/stubs/__init__.py

@@ -314,7 +314,7 @@ class VCRConnection:
     def __setattr__(self, name, value):
         """
         We need to define this because any attributes that are set on the
-        VCRConnection need to be propogated to the real connection.
+        VCRConnection need to be propagated to the real connection.
 
         For example, urllib3 will set certain attributes on the connection,
         such as 'ssl_version'. These attributes need to get set on the real