Delete travis.yml since travis is not used anymore

.travis.yml

@@ -1,26 +0,0 @@
-os:
-  - linux
-dist: trusty
-
-language: c
-
-cache:
-  directories:
-    - "$HOME/.choosenim"
-
-install:
-  - export CHOOSENIM_CHOOSE_VERSION="0.18.0"
-  - |
-      curl https://nim-lang.org/choosenim/init.sh -sSf > init.sh
-      sh init.sh -y
-  - export PATH=$HOME/.nimble/bin:$PATH
-
-before_script:
-  - set -e
-  - set -x
-
-script:
-  - nim c -d:ssl -r package_scanner.nim && node ./validate_json.js
-
-notifications:
-  email: false # noisy