extractors/mgtv: Adapt the new API

[iawia002]

fix #147

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@005c75e). Click here to learn what that means.
The diff coverage is 97.18%.

@@            Coverage Diff            @@
##             master     #148   +/-   ##
=========================================
  Coverage          ?   90.66%           
=========================================
  Files             ?       21           
  Lines             ?     1135           
  Branches          ?        0           
=========================================
  Hits              ?     1029           
  Misses            ?       82           
  Partials          ?       24

Impacted Files	Coverage Δ
extractors/tumblr.go	96.92% <100%> (ø)
extractors/mgtv.go	97.97% <100%> (ø)
extractors/miaopai.go	100% <100%> (ø)
extractors/twitter.go	83.33% <100%> (ø)
extractors/youtube/youtube.go	94.49% <100%> (ø)
extractors/douyin.go	100% <100%> (ø)
extractors/bcy.go	100% <100%> (ø)
extractors/vimeo.go	100% <100%> (ø)
extractors/facebook.go	100% <100%> (ø)
extractors/douyu.go	95.45% <100%> (ø)
... and 7 more

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