chore(example): add test case for source inclusion

This commit adds a manual test case that simulates accidently including
source files into the `files` and `preprocessor` section of the karma
configuration file.

Related to #52

example/karma.conf.js

@@ -7,12 +7,16 @@ module.exports = function(karma) {
 
     files: [
       'vendor/external.js',
+      // source file, accidently included
+      // (there is usually no reason to do this)
+      'lib/a.js',
       'test/**/*Spec.js'
     ],
 
     reporters: [ 'dots' ],
 
     preprocessors: {
+      'lib/*.js': [ 'browserify' ],
       'test/**/*Spec.js': [ 'browserify' ]
     },