gem: add solargraph support

lib/dyndnsd/database.rb

@@ -7,10 +7,12 @@ module Dyndnsd
 
     def_delegators :@db, :[], :[]=, :each, :has_key?
 
+    # @param db_file [String]
     def initialize(db_file)
       @db_file = db_file
     end
 
+    # @return [void]
     def load
       if File.file?(@db_file)
         @db = JSON.parse(File.open(@db_file, 'r', &:read))
@@ -20,6 +22,7 @@ module Dyndnsd
       @db_hash = @db.hash
     end
 
+    # @return [void]
     def save
       Helper.span('database_save') do |_span|
         File.open(@db_file, 'w') { |f| JSON.dump(@db, f) }
@@ -27,6 +30,7 @@ module Dyndnsd
       end
     end
 
+    # @return [Boolean]
     def changed?
       @db_hash != @db.hash
     end