support m4a file extension

[VICrazy]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

feature

⤵️ What is the current behavior?

The m4a audio file extension is not supported now.

🆕 What is the new behavior (if this is a feature change)?

The m4a audio file extension are already supported.

💥 Does this PR introduce a breaking change?

no

🐛 Recommendations for testing

Download the m4a audio file via http, and then play the file

📝 Links to relevant issues/docs

https://github.com/Baseflow/flutter_cache_manager/pull/172/files

🤔 Checklist before submitting

• All projects build
• Follows style guide lines (code style guide)
• Relevant documentation was updated
• Rebased onto current develop

[codecov]

Codecov Report

Merging #358 (ee9003e) into develop (aca37f6) will decrease coverage by 0.10%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #358      +/-   ##
===========================================
- Coverage    75.39%   75.28%   -0.11%     
===========================================
  Files           22       23       +1     
  Lines          691      692       +1     
===========================================
  Hits           521      521              
- Misses         170      171       +1     

Impacted Files	Coverage Δ
flutter_cache_manager/lib/src/cache_manager.dart	88.31% <ø> (ø)
.../lib/src/cache_managers/default_cache_manager.dart	0.00% <ø> (ø)
flutter_cache_manager/lib/src/cache_store.dart	92.55% <ø> (ø)
...he_manager/lib/src/compat/file_service_compat.dart	93.33% <ø> (ø)
...utter_cache_manager/lib/src/config/_config_io.dart	12.50% <ø> (ø)
flutter_cache_manager/lib/src/config/config.dart	0.00% <ø> (ø)
...tter_cache_manager/lib/src/web/mime_converter.dart	100.00% <ø> (ø)
flutter_cache_manager/lib/src/web/web_helper.dart	95.65% <ø> (ø)

---

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[renefloor]

Sorry about the analyzer, yours is the first PR since the new Flutter stable. If you want I can create a separate PR to fix the analyzer issues.

[VICrazy]

Sorry about the analyzer, yours is the first PR since the new Flutter stable. If you want I can create a separate PR to fix the analyzer issues.

Thanks, but I want to try fix it.