Add slather script

.slather.yml

+coverage_service: coveralls
+ci_service: travis_ci
+xcodeproj: iTerm2.xcodeproj
+ignore:
+  - "../**/Developer/*"
+  - "ThirdParty/*"
+  - "iTerm2XCTests/*"
+  - "Pods/*"

.travis.yml

@@ -3,3 +3,4 @@ bundler_args: --without documentation --without development --deployment --jobs=
 osx_image: xcode7.2
 language: objective-c
 script: ./ci/script.sh
+after_success: ./ci/after_success.sh

ci/after_success.sh

+#!/usr/bin/env bash
+
+set -euo pipefail
+
+bundle exec slather coverage \
+    --input-format profdata \
+    --scheme iTerm2 \
+    iTerm2.xcodeproj