gem: fix applicable rubocop todos

lib/dyndnsd/database.rb

@@ -4,27 +4,27 @@ require 'forwardable'
 module Dyndnsd
   class Database
     extend Forwardable
-    
+
     def_delegators :@db, :[], :[]=, :each, :has_key?
-  
+
     def initialize(db_file)
       @db_file = db_file
     end
-    
+
     def load
       if File.file?(@db_file)
-        @db = JSON.load(File.open(@db_file, 'r') { |f| f.read })
+        @db = JSON.parse(File.open(@db_file, 'r', &:read))
       else
         @db = {}
       end
       @db_hash = @db.hash
     end
-    
+
     def save
       File.open(@db_file, 'w') { |f| JSON.dump(@db, f) }
       @db_hash = @db.hash
     end
-    
+
     def changed?
       @db_hash != @db.hash
     end