Update wechaty requirement from ~=0.7dev16 to ~=0.8

Updates the requirements on [wechaty](https://github.com/wechaty/python-wechaty) to permit the latest version.
- [Release notes](https://github.com/wechaty/python-wechaty/releases)
- [Commits](https://github.com/wechaty/python-wechaty/commits)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

requirements.txt

@@ -1 +1 @@
-wechaty~=0.7dev16
+wechaty~=0.8