Turns out, travis doesn't support 8.3, reverting to 8.1 :(

.travis.yml

@@ -58,6 +58,3 @@ env:
 branches:
   only:
     - master
-
-xcode_sdk:
-  - iphonesimulator8.3

Examples/UIExplorer/UIExplorerTests/UIExplorerTests.m

@@ -38,11 +38,11 @@
   RCTAssert(!__LP64__, @"Snapshot tests should be run on 32-bit device simulators (e.g. iPhone 5)");
 #endif
   NSString *version = [[UIDevice currentDevice] systemVersion];
-  RCTAssert([version isEqualToString:@"8.3"], @"Snapshot tests should be run on iOS 8.3, found %@", version);
+  RCTAssert([version isEqualToString:@"8.1"], @"Snapshot tests should be run on iOS 8.1, found %@", version);
   _runner = RCTInitRunnerForApp(@"Examples/UIExplorer/UIExplorerApp");
 
   // If tests have changes, set recordMode = YES below and run the affected
-  // tests on an iPhone5, iOS 8.3 simulator.
+  // tests on an iPhone5, iOS 8.1 simulator.
   _runner.recordMode = NO;
 }