feat: get error logs from fail notifications.

[appleboy]

fix #109

[codecov-io]

Codecov Report

Merging #213 into master will decrease coverage by 0.01%.
The diff coverage is 87.17%.

@@            Coverage Diff             @@
##           master     #213      +/-   ##
==========================================
- Coverage   96.25%   96.23%   -0.02%     
==========================================
  Files          13       13              
  Lines         907      930      +23     
==========================================
+ Hits          873      895      +22     
- Misses         26       27       +1     
  Partials        8        8

Impacted Files	Coverage Δ
gorush/server.go	100% <100%> (ø)	⬆️
gorush/log.go	93% <70%> (+0.8%)	⬆️
gorush/notification.go	91.15% <92.59%> (-0.1%)	⬇️

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