Fix some bugs
What's Changed
* Update backends.py by chensgit169 in https://github.com/ScQ-Cloud/pyquafu/pull/41
* Update instruction.py by chensgit169 in https://github.com/ScQ-Cloud/pyquafu/pull/38
* Update tasks.py by chensgit169 in https://github.com/ScQ-Cloud/pyquafu/pull/40
* Update tasks.py by chensgit169 in https://github.com/ScQ-Cloud/pyquafu/pull/39
**Full Changelog**: https://github.com/ScQ-Cloud/pyquafu/compare/v0.3.2...v0.3.3