add a context return value from Stop function like cron.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 88.14%. Comparing base (b0e3dac) to head (2e95779).

Files	Patch %	Lines
dcron.go	66.66%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #100 +/- ## =========================================== - Coverage 88.24% 88.14% -0.10% =========================================== Files 17 17 Lines 1097 1097 =========================================== - Hits 968 967 -1 - Misses 98 99 +1 Partials 31 31 ```

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