Fix broken travis test (#490)

Summary:
The travis test used to terminate after 10 minutes of `pod install --silent` being unresponsive, added `travis_wait` to circumvent it.

## Changelog

Fixed the broken travis test
Pull Request resolved: https://github.com/facebook/flipper/pull/490

Test Plan: All tests are green on this PR.

Reviewed By: jknoxville

Differential Revision: D16261250

Pulled By: priteshrnandgaonkar

fbshipit-source-id: 323c5decb66232830d692b784f7cf5f9cbf67a01

.travis.yml

@@ -51,7 +51,7 @@ matrix:
       install:
         - cd iOS/Sample
         - rm -f Podfile.lock
-        - pod install --silent
+        - travis_wait pod install --silent
         - cd ../../
 
       script:
@@ -70,7 +70,7 @@ matrix:
       install:
         - cd iOS/SampleSwift
         - rm -f Podfile.lock
-        - pod install --silent
+        - travis_wait pod install --silent
         - cd ../../
       script:
         - cd iOS/SampleSwift