travis.yml: use 11.3 simulator to run tests

This commit uses an iOS 11.3 simultator to run the tests.

Author: r-mckay

.travis.yml

@@ -11,7 +11,7 @@ env:
     - WATCHOS_SDK="watchsimulator4.0"
     - FRAMEWORK="RxKeyboard"
   matrix:
-    - SDK="$IOS_SDK"      TEST=0  DESTINATION="platform=iOS Simulator,name=iPhone 8,OS=11.2"
+    - SDK="$IOS_SDK"      TEST=0  DESTINATION="platform=iOS Simulator,name=iPhone 8,OS=11.3"
 
 install:
   - eval "$(curl -sL https://gist.githubusercontent.com/kylef/5c0475ff02b7c7671d2a/raw/9f442512a46d7a2af7b850d65a7e9bd31edfb09b/swiftenv-install.sh)"