Initial continuous integration

* Work towards resolving #1346
* package json: add empty test (run by travisCI by default)
* add minimal .travis.yml

.travis.yml

@@ -0,0 +1,7 @@
+language: node_js
+node_js:
+  - '5'
+sudo: false
+script:
+  - npm install
+  - npm test

package.json

@@ -23,5 +23,8 @@
     "type": "git",
     "url": "git://github.com/mathjax/MathJax.git"
   },
-  "main": "./MathJax.js"
+  "main": "./MathJax.js",
+  "scripts": {
+    "test": "echo 'No tests here!'"
+  }
 }