Move before_install steps to a separate script

.travis.yml

@@ -1,14 +1,5 @@
 sudo: false
-before_install:
-  - git fetch origin master:master
-  - git fetch origin v2.0.0:v2.0.0
-  - git fetch origin test/attributes:test/attributes
-  - git fetch origin test/master:test/master
-  - script/vendor-deb libicu48 libicu-dev
-  - bundle config build.charlock_holmes --with-icu-include=$(pwd)/vendor/debs/include --with-icu-lib=$(pwd)/vendor/debs/lib
-  - git submodule init
-  - git submodule sync --quiet
-  - script/fast-submodule-update
+before_install: script/travis/before_install
 rvm:
   - 1.9.3
   - 2.0.0