[CI] Use xcode 8.3 and our own installation and test scripts

Author: isair

.travis.yml

@@ -1,2 +1,6 @@
 language: objective-c
-osx_image: xcode7.1
+osx_image: xcode8.3
+install:
+  - ./scripts/install-travis.sh
+script:
+  - ./scripts/test.sh

scripts/install-travis.sh

@@ -0,0 +1,7 @@
+#! /bin/sh
+
+# Initialize project
+
+cd "$(dirname "$0")/.."
+
+bundle install --path vendor/bundle