fix: add 'requests.exceptions.ChunkedEncodingError' to retryable exceptions (#237)

Closes #235.
diff --git a/google/api_core/retry.py b/google/api_core/retry.py
index f0f23bc..8496793 100644
--- a/google/api_core/retry.py
+++ b/google/api_core/retry.py
@@ -104,6 +104,7 @@
     exceptions.TooManyRequests,
     exceptions.ServiceUnavailable,
     requests.exceptions.ConnectionError,
+    requests.exceptions.ChunkedEncodingError,
     auth_exceptions.TransportError,
 )
 """A predicate that checks if an exception is a transient API error.
diff --git a/tests/unit/test_retry.py b/tests/unit/test_retry.py
index f24c82b..199ca55 100644
--- a/tests/unit/test_retry.py
+++ b/tests/unit/test_retry.py
@@ -45,6 +45,7 @@
     assert retry.if_transient_error(exceptions.TooManyRequests(""))
     assert retry.if_transient_error(exceptions.ServiceUnavailable(""))
     assert retry.if_transient_error(requests.exceptions.ConnectionError(""))
+    assert retry.if_transient_error(requests.exceptions.ChunkedEncodingError(""))
     assert retry.if_transient_error(auth_exceptions.TransportError(""))
     assert not retry.if_transient_error(exceptions.InvalidArgument(""))