Fix typo in search box placeholder

Refs pombase/pombase-gocam#142

Author: kimrutherford

gocam_view/templates/gocam_view/index.html

@@ -1262,7 +1262,7 @@
 <div id="cy-panel">
 {% if full_or_widget == 'full' %}
   <div id="search-box" style="display: none">
-    <input id="search-input" width="30" placeholder="Search for activies or models ..."/>
+    <input id="search-input" width="30" placeholder="Search for activities or models ..."/>
   </div>
 {% endif %}
   <div id="cy-panel-contents">