Fix lint

bin/mmdb-benchmark.rb:6:5: C: Naming/PredicateMethod: Predicate method names should end with ?.
def main
    ^^^^

Author: horgh

.rubocop.yml

@@ -14,6 +14,10 @@ Layout/LineLength:
 Metrics/MethodLength:
     Enabled: false
 
+Naming/PredicateMethod:
+    AllowedMethods:
+        - main
+
 # Weird.
 Style/FormatStringToken:
     Enabled: false