[rack-protection] drop unused Travis config

rack-protection/.travis.yml

@@ -1,34 +0,0 @@
----
-language: ruby
-
-dist: trusty
-sudo: false
-
-before_install:
-  - rvm get head
-  - gem install bundler
-
-rvm:
-  - 2.2.4
-  - 2.3.1
-  - ruby-head
-  - rbx
-  - jruby-9.1.0.0
-  - jruby-head
-
-matrix:
-  include:
-    - { rvm: 2.3.1,         env: rack=stable }
-    - { rvm: 2.3.1,         env: rack=master }
-    - { rvm: jruby-head,    env: rack=master }
-    - { rvm: ruby-head,     env: rack=master }
-  allow_failures:
-    - env: rack=master
-    - rvm: jruby-head
-    - rvm: ruby-head
-    - rvm: rbx
-
-notifications:
-  recipients:
-    - mail@zzak.io
-  slack: sinatrarb:LQGhUfGYcqRgRzwKea0bqUhY