Remove .travis.yml file

- no reason to build or test Windows-only WebListener on Linux or OS X

.travis.yml

@@ -1,26 +0,0 @@
-language: csharp
-sudo: required
-dist: trusty
-addons:
-  apt:
-    packages:
-    - gettext
-    - libcurl4-openssl-dev
-    - libicu-dev
-    - libssl-dev
-    - libunwind8
-    - zlib1g
-mono:
-  - 4.0.5
-os:
-  - linux
-  - osx
-osx_image: xcode7.1
-branches:
-  only:
-    - master
-    - release
-    - dev
-    - /^(.*\/)?ci-.*$/
-script:
-  - ./build.sh verify