Function ensureTrailingSlash

ensureTrailingSlash(str: string): string
Ensure trailing slash, if str does not end with slash, it will be added

确保后缀，如果字符串不以斜杠结尾，则将添加斜杠
Parameters
- str: string
  The string to ensure trailing slash. / 要确保后缀的字符串
Returns string
The string with trailing slash. / 确保后缀后的字符串
Example
```
ensureTrailingSlash('/foo/bar') // => /foo/bar/
```
- Defined in src/url/slash.ts:58