Spring fix timezone parsing

Comment From: snicoll

@yibijianghu thanks for the PR but you haven't described what this code change is supposed to fix. And we can't really consider it until you do with unit tests.

Comment From: yibijianghu

if timeZoneString is "GMTabc"， this method will return GMT. but if timeZoneString is "abc", it will throw IllegalArgumentException. this is not right. GMTabc or abc should throw exception.

Comment From: snicoll

this is not right. GMTabc or abc should throw exception.

@yibijianghu the Javadoc of parseTimeZoneString states:

timeZoneString – the time zone String, following TimeZone. getTimeZone(String) [...]

So it's working as documented. TimeZone.getTimeZone("GMTabc") returns GMT indeed and that's a behavior of the JDK.