ionic 2.0.0-alpha.54 发布，更新如下： Bug 修复 alert: add checkbox icon for iOS using Sass variables from regular checkbox (68819f0), closes #5253 badge: change default badge color to primary (93b9891), closes #5222 badge: split badge color into separate modes (b472c6c) css: minor updates to match previous snapshots (9749b06) input: add/remove disabled on native text input (11b8e08), closes #5280 input: check has value on writeValue (181a070) input: parent Item is optional (db6f4bc) prepare: add missing require to prepare task (b2f7278) scrollbars: do not apply css scrollbars (f3fb182) select: always update value and text (58443f0) select: null value clears select text (c264e31), closes #5288 特性 button: increase hit area of toolbar buttons (cad9e49) checkbox: add bg transition to md checkbox (8466d39) overlay: fire the cancel handler when dismissing from backdrop (1c618b5) scrollbars: webkit scrollbar styling for desktop (c7f2268) 下载页面：2.0.0-alpha.54 ionic 2.0.0-alpha.54 发布，移动应用框架下载地址
