Travis CI improvements

 - Cache NPM modules across builds
 - Don't run Sauce Labs tests for pull requests

Author: Andy Earnshaw

.travis.yml

@@ -8,3 +8,9 @@ addons:
     username: andyearnshaw
     access_key:
       secure: 'OslPEaqVgNH+9YWwtEIJE4/Ot+RmSonIYMxvxMjnaaLAkoYX34nJzaB8vPFP1txDwkDHpOy+MiQ8hKYhyilw5Ydr11O2IEuhVjcJThKSoN3yMTe6FHpXQKO9uC1loaRwJs2uV0go+P4ooywZ8Y72/RtKXk0OOhn5Lg5ekb3wMRg='
+
+cache:
+  directories:
+    - node_modules
+
+sudo: false

tests/saucelabs.js

@@ -446,7 +446,12 @@ function main(tunnelReady) {
 // Save the current cursor position for redraws
 drawStatus();
 
-if (tunnel) {
+// Avoid "The Travis CI build failed" message on PRs
+if (process.env.TRAVIS_PULL_REQUEST) {
+    console.warn('Unable to run Sauce Labs tests for pull requests.');
+    process.exit(0);
+}
+else if (tunnel) {
     tunnel.start(main);
     tunnel.proc.stdout.on('data', function (msg) {
         lastTunnelMessage = String(msg).split('\n').shift();