Fixed invalid spelling, backend -> back-end (#130)

Author: Anders Breid

src/main/resources/templates/index.html

@@ -67,14 +67,14 @@
         <li id="adminBackendInstancesBtn" class="nav-item">
           <a class="nav-link nav-link-collapse" data-toggle="collapse" href="#collapseBackEndPages" data-parent="#exampleAccordion">
             <i class="fa fa-fw fa-file"></i>
-            <span class="nav-link-text">Administration backend instances</span>
+            <span class="nav-link-text">Administration back-end instances</span>
           </a>
           <ul class="sidenav-second-level collapse" id="collapseBackEndPages">
             <li>
-              <a id="addInstanceBtn" href="#add-backend" data-navigo>Add backend instance</a>
+              <a id="addInstanceBtn" href="#add-backend" data-navigo>Add back-end instance</a>
             </li>
             <li>
-              <a id="switcherBtn" href="#switch-backend" data-navigo>Switch backend instance</a>
+              <a id="switcherBtn" href="#switch-backend" data-navigo>Switch back-end instance</a>
             </li>
           </ul>
         </li>