tomcat中止时，日志failed to remove it when the web application was stopped.

• 最近查看项目日志，发现tomcat中止时，会以下报错：

The web application created a ThreadLocal with key of type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal@1fb9b07e]) and a value of type [io.netty.util.internal.InternalThreadLocalMap] (value [io.netty.util.internal.InternalThreadLocalMap@2c86e33e]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak

找了不少地方，发现这个日志是能够忽略，若是真须要日志再也不显示，能够参考：

1. https://github.com/netty/netty/issues/2084
2. https://github.com/relayrides/pushy/issues/29