`decirc` seems to fail for circular getter attributes#44

Hi there! We've found an issue when calling the stringify function where there are circular references in a getter. Example: ```javascript const fastSafeStringify = require('fast-safe-stringify') const o = { a: 1, get self() { return o }, } console.log(fastSafeStringify(o)) ``` Which throws the following error: ``` /Users/kristofferostlund/dev/logger-node/examples/node_modules/fast-safe-stringify/index.js:11 var res = JSON.stringify(obj, replacer, spacer) ^ TypeError: Converting circular structure to JSON at JSON.stringify (<anonymous>) at stringify (/Users/kristofferostlund/dev/logger-node/examples/node_modules/fast-safe-stringify/index.js:11:18) at Object.<anonymous> (/Users/kristofferostlund/dev/logger-node/examples/circular-meta-example.js:57:13) at Module._compile (module.js:653:30) at Object.Module._extensions..js (module.js:664:10) at Module.load (module.js:566:32) at tryModuleLoad (module.js:506:12) at Function.Module._load (module.js:498:3) at Function.Module.runMain (module.js:694:10) at startup (bootstrap_node.js:204:16) ```