Enable SwiftLint rule 'legacy_multiple' and fix all violations

.swiftlint.yml

@@ -86,7 +86,7 @@ whitelist_rules:
   - legacy_constant
   - legacy_constructor
   - legacy_hashing
-#  - legacy_multiple
+  - legacy_multiple
   - legacy_nsgeometry_functions
   - legacy_random
 #  - let_var_whitespace

passKit/Passwords/PasswordGenerator.swift

@@ -76,7 +76,7 @@ public struct PasswordGenerator: Codable {
         guard flavor == .random, groups > 0, groups < length else {
             return false
         }
-        return (length + 1) % groups == 0
+        return (length + 1).isMultiple(of: groups)
     }
 
     private func generateRandom() -> String {