'build' grunt task was renamed to 'fetch'. Updated docs

docs/html/_sources/index.txt

@@ -234,7 +234,7 @@ Now that we have Grunt and Bower, you can install and configure Converse's
 
 ::
 
-    grunt build
+    grunt fetch
 
 With AMD and require.js (recommended)
 =====================================

docs/html/index.html

@@ -277,7 +277,7 @@ directory:</p>
 <h2><a class="toc-backref" href="#id12">Install 3rd party dependencies</a><a class="headerlink" href="#install-3rd-party-dependencies" title="Permalink to this headline">¶</a></h2>
 <p>Now that we have Grunt and Bower, you can install and configure Converse&#8217;s
 3rd party dependencies with the following command:</p>
-<div class="highlight-python"><pre>grunt build</pre>
+<div class="highlight-python"><pre>grunt fetch</pre>
 </div>
 </div>
 <div class="section" id="with-amd-and-require-js-recommended">

docs/source/index.rst

@@ -234,7 +234,7 @@ Now that we have Grunt and Bower, you can install and configure Converse's
 
 ::
 
-    grunt build
+    grunt fetch
 
 With AMD and require.js (recommended)
 =====================================