docs(modal): make dialog demo closable

src/dialog/styles/_common.ts

@@ -6,7 +6,7 @@ export default {
   contentMargin: '8px 0 16px 0',
   iconMargin: '0 4px 0 0',
   iconMarginIconTop: '4px 0 8px 0',
-  closeSize: '16px',
+  closeSize: '18px',
   closeMargin: '22px 28px 0 0',
   closeMarginIconTop: '12px 18px 0 0'
 }

src/modal/demos/enUS/preset-confirm.demo.md

@@ -9,7 +9,6 @@ An example of preset `dialog`.
   preset="confirm"
   title="Dialog"
   content="Are you sure?"
-  :closable="false"
   positive-text="Submit"
   @positive-click="submitCallback"
   @negative-click="cancelCallback"

src/modal/demos/zhCN/preset-confirm.demo.md

@@ -9,7 +9,6 @@
   preset="confirm"
   title="确认"
   content="你确认?"
-  :closable="false"
   positive-text="确认"
   @positive-click="submitCallback"
   @negative-click="cancelCallback"