chore(deps): update dependency twilio to v6.45.0 (GoogleCloudPlatform#4570)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [twilio](https://togithub.com/twilio/twilio-python) | minor | `==6.44.2` -> `==6.45.0` |

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### Release Notes

<details>
<summary>twilio/twilio-python</summary>

### [`v6.45.0`](https://togithub.com/twilio/twilio-python/blob/master/CHANGES.md#&#8203;2020-08-19-Version-6450)

[Compare Source](https://togithub.com/twilio/twilio-python/compare/6.44.2...6.45.0)

**Library - Chore**

-   [PR #&GoogleCloudPlatform#8203;536](https://togithub.com/twilio/twilio-python/pull/536): update GitHub branch references to use HEAD. Thanks to [@&GoogleCloudPlatform#8203;thinkingserious](https://togithub.com/thinkingserious)!

**Conversations**

-   Allow Identity addition to Participants

**Events**

-   Sinks API Get all Sinks

**Proxy**

-   Clarified usage of FailOnParticipantConflict param as experimental
-   Add FailOnParticipantConflict param to Proxy Session create and Proxy Participant create

**Supersim**

-   Add fleet, network, and isoCountryCode to the UsageRecords resource
-   Change sort order of UsageRecords from ascending to descending with respect to start time field, records are now returned newest to oldest

**Wireless**

-   Removed `Start` and `End` parameters from the Data Sessions list endpoint. **(breaking change)**

</details>

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appengine/flexible/twilio/requirements.txt

@@ -1,3 +1,3 @@
 Flask==1.1.2
 gunicorn==20.0.4
-twilio==6.44.2
+twilio==6.45.0