fix: remove reference to Bower (#860)

Remove reference to Bower, as Bower now recommends using Yarn

Author: ThomasRedstone

app/index.html

@@ -53,7 +53,7 @@ <h1>What's Yeoman?</h1>
         <h2>Tools</h2>
 
         <p>
-          The Yeoman workflow comprises three types of tools for improving your productivity and satisfaction when building a web app: the scaffolding tool (yo), the build tool (npm scripts, Gulp, Grunt etc) and the package manager (like npm and Bower).
+          The Yeoman workflow comprises three types of tools for improving your productivity and satisfaction when building a web app: the scaffolding tool (yo), the build tool (npm scripts, Gulp, Grunt etc) and the package manager (like npm and Yarn).
         </p>
 
         <ul class="basic-tools clearfix">