fix require statement for including build/watch tasks

When requiring a file module relative to the calling file, path needs to be prefixed with "./".
See Semantic-Org/Semantic-UI#2653

server/documents/introduction/advanced-usage.html.eco

@@ -18,8 +18,8 @@ type        : 'Introduction'
     <p>You don't have to use <a href="/introduction/build-tools.html">our gulp pipeline</a>, just import the task into your own <code>gulpfile</code></p>
     <div class="ignored code" data-type="JS" data-title="Custom gulpfile.js">
     var
-      watch = require('semantic/tasks/watch'),
-      build = require('semantic/tasks/build')
+      watch = require('./semantic/tasks/watch'),
+      build = require('./semantic/tasks/build')
     ;
     // import task with a custom task name
     gulp.task('watch ui', 'Watch Semantic UI', watch));
@@ -166,4 +166,4 @@ type        : 'Introduction'
     <p>Doc task paths are specified in a file <a href="https://github.com/Semantic-Org/Semantic-UI/blob/master/tasks/config/docs.js"><code>tasks/config/docs.js</code></a> and can be adjusted to use any folder set-up necessary for your project.</p>
   </div>
 
-</div>
+</div>