notify travis status in servo-bots channel

[edunham]

this is the other half of fixing #376

i have already turned on nightly builds via travis's experimental cron feature

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This change is 

[aneeshusa]

What is the #servo-bots channel? Is there someone (a human) monitoring this so we find out about failed nightly builds?

[edunham]

#servo-bots is a channel where all of Servo's bots dump information, so that we can use our IRC clients to filter those notifications which we care about. Jack and I idle in there, and others are welcome to as well.

Dropping notifications into the bots channel basically just makes it easy to "subscribe" to whatever subset of notifications we each find relevant, while making sure we don't clutter the channels which exist for human conversation.

[aneeshusa]

OK, the only other suggestion I had was maybe using on_success and on_failure to pre-filter which notifications Travis sends to IRC, but if you're filtering in your client it's not necessary. r=me with or without that.

[edunham]

@bors-servo r=aneeshusa

[bors-servo]

📌 Commit b4adc55 has been approved by aneeshusa

[bors-servo]

⌛ Testing commit b4adc55 with merge 8c9aa37...

[bors-servo]

☀️ Test successful - status-travis
Approved by: aneeshusa
Pushing 8c9aa37 to master...