Changes

Fix IllegalArgumentException on TextChannel#canTalk()
Since the `guild` field is now an `UpstreamReference`, directly
comparing it to a Guild object results in an error:
```java
the Guild that this TextChannel is part of.
at
net.dv8tion.jda.core.entities.impl.TextChannelImpl.canTalk(TextChannelImpl.java:182)

at
net.dv8tion.jda.core.entities.impl.TextChannelImpl.canTalk(TextChannelImpl.java:175)

```
 (commit: 4b63e62)