.travis.yml: Check GITHUB_TOKEN before deploy

Provide a helpful error message early in build when
pushing to master without deploy variable GITHUB_TOKEN.

Closes #60

Author: jayvdb

.ci/check_travis_deploy_vars.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+set -ex
+
+if [[ $TRAVIS_BRANCH == master && $TRAVIS_EVENT_TYPE == push && 
+      ! "$GITHUB_TOKEN" ]]; then
+  echo "Please set GITHUB_TOKEN in your Travis CI environment settings"
+  false
+fi

.travis.yml

@@ -47,6 +47,7 @@ jobs:
       script: coala --non-interactive -V
 
 before_install:
+  - .ci/check_travis_deploy_vars.sh
   - npm config set spin false
 
 before_script: