Deprecate gems configuration option to use plugins
Deprecate gems configuration option to use plugins

In Jekyll 3.6.0, this change is to suppress the following warning:
```
Deprecation: The 'gems' configuration option has been renamed to 'plugins'. Please update your config file accordingly.
```
itCatface/itcatface.github.io,aar0u/aar0u.github.io,danieldaydan/danieldaydan.github.io,Huxpro/huxpro.github.io,luopeixiang/luopeixiang.github.io,VernonSong/VernonSong.github.io,NominationP/NominationP.github.io,Huxpro/huxpro.github.io,Huxpro/huxpro.github.io,rongfeng-china/rongfeng-china.github.io,wizecore/wizecore.github.io,liangyulai/liangyulai.github.io,danieldaydan/danieldaydan.github.io,danieldaydan/danieldaydan.github.io,NominationP/NominationP.github.io,itCatface/itcatface.github.io,DavidZliu/DavidZliu.github.io,aar0u/aar0u.github.io,jobn123/jobn123.github.io,shinyzhu/shinyzhu.github.io,pingyourid/pingyourid.github.io,Laciann/Laciann.github.io,aar0u/aar0u.github.io,shinyzhu/shinyzhu.github.io,gouaili/gouaili.github.io,wizecore/wizecore.github.io,luopeixiang/luopeixiang.github.io,VernonSong/VernonSong.github.io,Laciann/Laciann.github.io,NominationP/NominationP.github.io,txyafx/txyafx.github.io,rongfeng-china/rongfeng-china.github.io,qiulin/qiulin.github.io,pingyourid/pingyourid.github.io,gouaili/gouaili.github.io,txyafx/txyafx.github.io,jobn123/jobn123.github.io,qiulin/qiulin.github.io,shinyzhu/shinyzhu.github.io,liangyulai/liangyulai.github.io,shinyzhu/shinyzhu.github.io,wizecore/wizecore.github.io,rongfeng-china/rongfeng-china.github.io,wizecore/wizecore.github.io