Supporting structure of flex sensor is caught by suction finger in pinching

[pazeshun]

This is similar problem as #2165 , but not fatal because this doesn't break fingers.
But I have to fix this as this prevents pinching small objects.
Fortunately, improved finger is already made, so I'll replace.

[pazeshun]

I'll postpone this because #2214 has higher priority

[pazeshun]

• Print additional fingers (~1 day)
• Mold rubber to fingers (~2 days)

[pazeshun]

こちらですが、現状そこまで問題になっていないのと、直す時間がなさそうなので、指が壊れた時の部品交換時に直すことにします。