fix misspelled "occured" to "occurred"

Reference: http://www.gingersoftware.com/english-online/spelling-book/misspelling/occurred-occured-ocurred

assets/javascripts/templates/error_tmpl.coffee

@@ -37,10 +37,10 @@ app.templates.offlineError = (reason, exception) ->
       """ Your browser appears to be running in private mode.<br>
           This prevents DevDocs from caching documentations for offline access."""
     when 'exception'
-      """ An error occured when trying to open the IndexedDB database:<br>
+      """ An error occurred when trying to open the IndexedDB database:<br>
           <code class="_label">#{exception.name}: #{exception.message}</code> """
     when 'cant_open'
-      """ An error occured when trying to open the IndexedDB database:<br>
+      """ An error occurred when trying to open the IndexedDB database:<br>
           <code class="_label">#{exception.name}: #{exception.message}</code><br>
           This could be because you're browsing in private mode or have disallowed offline storage on the domain. """
     when 'version'

assets/javascripts/templates/notif_tmpl.coffee

@@ -13,7 +13,7 @@ app.templates.notifUpdateReady = ->
             """<span data-behavior="reboot"><a href="#" data-behavior="reboot">Reload the page</a> to use the new version.</span>"""
 
 app.templates.notifError = ->
-  textNotif """ Oops, an error occured. """,
+  textNotif """ Oops, an error occurred. """,
             """ Try <a href="#" data-behavior="hard-reload">reloading</a>, and if the problem persists,
                 <a href="#" data-behavior="reset">resetting the app</a>.<br>
                 You can also report this issue on <a href="https://github.com/Thibaut/devdocs/issues/new" target="_blank" rel="noopener">GitHub</a>. """
@@ -31,7 +31,7 @@ app.templates.notifInvalidLocation = ->
             """ Otherwise things are likely to break. """
 
 app.templates.notifImportInvalid = ->
-  textNotif """ Oops, an error occured. """,
+  textNotif """ Oops, an error occurred. """,
             """ The file you selected is invalid. """
 
 app.templates.notifNews = (news) ->