Bump xcode version in travis config

[wiruzx]

No description provided.

[codecov-commenter]

Codecov Report

Merging #661 into master will increase coverage by 0.37%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #661      +/-   ##
==========================================
+ Coverage   73.01%   73.38%   +0.37%     
==========================================
  Files          19       19              
  Lines        1219     1236      +17     
==========================================
+ Hits          890      907      +17     
  Misses        329      329              

Impacted Files	Coverage Δ
Chatto/Source/SerialTaskQueue.swift	100.00% <0.00%> (ø)
...oller/Collaborators/ChatItemPresenterFactory.swift	100.00% <0.00%> (ø)
...ChatController/Collaborators/KeyboardTracker.swift	64.05% <0.00%> (+0.47%)	⬆️
...Source/ChatController/BaseChatViewController.swift	71.11% <0.00%> (+0.94%)	⬆️
...atto/Source/Chat Items/BaseChatItemPresenter.swift	51.02% <0.00%> (+1.02%)	⬆️
...ntroller/Collaborators/AccessoryViewRevealer.swift	34.61% <0.00%> (+2.61%)	⬆️

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