chore(travis): move log files to /tmp

Getting permission denied errors on Travis when trying to create
`/logs` directory. Couldn’t find any detailed docs on this, but `/tmp`
should be allowed.

.travis.yml

@@ -4,17 +4,18 @@ node_js:
 before_install:
   - 'npm install -g bower grunt-cli'
 before_script:
-  - mkdir -p '/logs'
+  - mkdir -p $LOGS_DIR
   - 'export DISPLAY=:99.0'
   - 'sh -e /etc/init.d/xvfb start'
 script:
   - 'npm test'
   - 'npm run coveralls'
   - 'npm run saucelabs'
 after_script:
-  - 'cat /logs/karma.log'
+  - 'cat $LOGS_DIR/karma.log'
 env:
   global:
+    - LOGS_DIR=/tmp/logs
     - secure: L+EPka9O38GaLwg3xqr6p9rwvwy4MnQH0Fba8Qlt1M5QzLRz3e9JdVvxCQrQlETR5Guc5CN1dLOQFhVyYoCFNcOs3VkeD/mnegq16LwFE9vcmxySRqleUja3eCQ4HQJP99pSiCHYQVGvoZUf82nYNz6bh7JusbGapyyUF4Nl1TU=
     - secure: l7fKnvanXbaLGAhlwyFRgNsSy8H5O13nbAU1AujLy9sP5tHnjHjvNLklV+wHw929h2L3pLi0OCMthDQPyA+4LnTNix6UW2f7p1tOwAxOqEWUSitWHway1pNOR9CZbpGVfdcoML/RGNgt1iwtEC9TyhxhbFw1pGZj8GLfCOVdthk=
 addons:

karma.conf.js

@@ -133,7 +133,7 @@ module.exports = function(config) {
 		// Debug logging into a file, that we print out at the end of the build.
 		config.loggers.push({
 			type: 'file',
-			filename: '/logs/karma.log'
+			filename: (process.env.LOGS_DIR || '') + '/logs/karma.log'
 		});
 	}
 };