[Validator] added ratio precision to image validator

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

In my current project I've added validation rule, that image aspect ratio should be equal `1.33`. But php gives more precision if calculate `4/3`. So I have to add hack: `minRatio="1.332", maxRatio="1.334"`.
This PR allow specify precision for image aspect ratio, using `ratioPrecision` option.