Increased max tweet length to 280

[RyanBluth]

Problem

The maximum tweet length is still set to 140 when it should be 280

Solution

Increased the max length

Result

Tested composing a tweet and there is no unexpected change in behavior

[CLAassistant]

All committers have signed the CLA.

[joeuelk]

I noticed the Twitter character count still shows 140 instead of 280 when using TWTRComposer() on TwitterKit 3.4.2.