Fixed corrupted servlet init() method, and 1 more.

• bugfix: fixed corrupted servlet init() method, sorry it is my wok.
• bugfix: fixed a misspelling.

This will fix getServletContext() throwing a NullPointerException.
Not very ergent to migrate to this version, in situation that you never encountered such an exception.

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• bugfix: 修正了 所有 servlet 的init() 方法, 以保证 getServletContext() 不会抛出 NullPointerException. (我的锅)
• bugfix: 异常信息的拼写错误.

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