resolves #260
Merge pull request #259 from yositani2002/reference/forms/types/collection.rst

[翻訳]reference/forms/types/collection.rst
二重バッククオートでtrueを囲みました。
Merge pull request #261 from yositani2002/reference/forms/types/options/error_bubbling.rst.inc

[翻訳]reference/forms/types/options/error_bubbling.rst.inc
[reference/constraints/Expression] Expression制約の翻訳 resolves #263
マークアップの修正。半角スペースを追加など。