chore(deps): update dependency rsa to <4.6 (#544)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [rsa](https://stuvel.eu/rsa) | minor | `<4.1` -> `<4.7` |

---

### Renovate configuration

:date: **Schedule**: At any time (no schedule defined).

:vertical_traffic_light: **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

:recycle: **Rebasing**: Renovate will not automatically rebase this PR, because other commits have been found.

:no_bell: **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [WhiteSource Renovate](https://renovate.whitesourcesoftware.com). View repository job log [here](https://app.renovatebot.com/dashboard#googleapis/google-auth-library-python).

setup.py

@@ -21,9 +21,10 @@
 DEPENDENCIES = (
     "cachetools>=2.0.0,<5.0",
     "pyasn1-modules>=0.2.1",
-    # rsa >= 4.1 no longer supports python 2 https://github.com/sybrenstuvel/python-rsa/issues/152
-    'rsa<4.1; python_version < "3"',
-    'rsa>=3.1.4,<5; python_version >= "3"',
+    # rsa==4.5 is the last version to support 2.7
+    # https://github.com/sybrenstuvel/python-rsa/issues/152#issuecomment-643470233
+    'rsa<4.6; python_version < "3.5"',
+    'rsa>=3.1.4,<5; python_version >= "3.5"',
     "setuptools>=40.3.0",
     "six>=1.9.0",
 )