replace `is_multi_check?` with `multi_check?`

lib/system_check/base_check.rb

@@ -73,7 +73,7 @@ module SystemCheck
       self.class.instance_methods(false).include?(:skip?)
     end
 
-    def is_multi_check?
+    def multi_check?
       self.class.instance_methods(false).include?(:multi_check)
     end
 

lib/system_check/simple_executor.rb

@@ -53,7 +53,7 @@ module SystemCheck
       end
 
       # When implements a multi check, we don't control the output
-      if check.is_multi_check?
+      if check.multi_check?
         check.multi_check
         return
       end