fix:dynamic mention options do not always load

[Gylllll]

#36

问题复现：

按下 shift ，再按下 @

此时分两种情况：

1. 先抬起 @ ，再抬起 shift ，则可以正常显示选项
2. 反之，先抬起 shift ，再抬起 @ ，则无法显示选项

期望：无论先抬起@，还是先抬起shift，都应正常显示选项

已解决该问题

[codecov]

Codecov Report

Merging #36 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #36   +/-   ##
=======================================
  Coverage   99.12%   99.12%           
=======================================
  Files           6        6           
  Lines         228      229    +1     
  Branches       50       51    +1     
=======================================
+ Hits          226      227    +1     
  Misses          2        2           

Impacted Files	Coverage Δ
src/Mentions.tsx	99.28% <100.00%> (+<0.01%)	⬆️

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