make 'script:' in .travis.yml do everything.

Previously I had it doing additional testing via the 'after_success:'
option, but if those scripts failed, they wouldn't fail the build.
Let's do everything in 'script:'.

.travis.yml

@@ -1,7 +1,2 @@
 language: objective-c
-script: ./build.sh
-after_success:
-  - # With xctool built, now build and test xctool using xctool...
-  - ./xctool.sh -workspace xctool.xcworkspace -scheme xctool build
-  - ./xctool.sh -workspace xctool.xcworkspace -scheme xctool build-tests
-  - ./xctool.sh -workspace xctool.xcworkspace -scheme xctool run-tests
+script: ./build.sh && ./xctool.sh -workspace xctool.xcworkspace -scheme xctool build build-tests run-tests