fixed typo

[Validator] [FrameworkBundle]  fixed a typo in farsi translation of length validator when input must be of exact size.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        |