util/ts:fix getDate,getSignature

[imbooo]

1、修复getDate，在moment没有设置时区的情况下，format的日期具有时差。
2、修复getSignature，在POST请求中，没有query参数情况下，slice会导致resource少一位。
3、添加header默认Content-Type，避免在GET请求时，getSignedStr中没有内容，导致签名验证失败。

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❌ wenzuochao
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