[SwiftLint] Remove identifier_name from disabled_rules

[ikesyo]

Ref: #370

[sharplet]

This seems fine to me. I'm guessing there's no swiftlint option to allow starting a variable name with an underscore?

[ikesyo]

I think so, looks like starting from an underscore is not permitted now:

• https://github.com/realm/SwiftLint/blob/master/Source/SwiftLintFramework/Rules/IdentifierNameRule.swift
• https://github.com/realm/SwiftLint/blob/master/Source/SwiftLintFramework/Rules/IdentifierNameRuleExamples.swift
• https://github.com/realm/SwiftLint/blob/master/Source/SwiftLintFramework/Rules/RuleConfigurations/NameConfiguration.swift

[ikesyo]

Disabling validates_start_with_lowercase option will be an option (but will not be preferable).

[ikesyo]

Probably related issues:

• Allow '_' both in variable names and type names realm/SwiftLint#628
• Non ascii operators are rejected by identifier_name for not starting with a lowercase letter. realm/SwiftLint#1762
• identifier_name rule doesn't respect allowed_symbols configuration option for functions realm/SwiftLint#1852

[ikesyo]

I'll merge this as is for now. Thanks for the review @sharplet!