docs: fix english quotation conflict (#1909)

Author: A81N9

packages/varlet-ui/src/snackbar/docs/en-US.md

@@ -141,7 +141,7 @@ import { Snackbar } from '@varlet/ui'
 </script>
 
 <template>
-  <var-button type="warning" block @click="Snackbar('Hello, I'm a snackbar')">Basic Usage</var-button>
+  <var-button type="warning" block @click="Snackbar('Hello, I\'m a snackbar')">Basic Usage</var-button>
 </template>
 ```