Fix import_json view

This view is returning a 500 on production because a bad
`render_to_response` call:
    https://sentry.io/columbia-ctl/uelc/issues/279731846/

I've replaced `render_to_response` with `render` in a previous commit,
but the call was still bad - I needed to remove the context_instance
argument, it's not necessary since the plain request is passed in to
render().

CHANGES.txt

@@ -1,3 +1,8 @@
+1.3.2
+==================
+
+* Fixed an issue with the json import view
+
 1.3.1 (2017-03-22)
 ==================
 

pagetree/views.py

@@ -3,7 +3,6 @@
 from django.http import HttpResponse, HttpResponseRedirect
 from django.utils.encoding import smart_text
 from django.shortcuts import get_object_or_404, render
-from django.template.context import RequestContext
 from django.template.defaultfilters import slugify
 from django.template.response import TemplateResponse
 from json import dumps, loads
@@ -80,8 +79,7 @@ def import_pageblock_json(request, pageblock_id):
         block.import_from_dict(json)
         return HttpResponseRedirect(block.section.get_edit_url())
     else:
-        return render(request, "import_json.html", dict(),
-                      context_instance=RequestContext(request))
+        return render(request, "import_json.html")
 
 
 def edit_pageblock(request, pageblock_id, success_url=None):