[1.7.x] Insert space.

Backport of 8eb51a8c from master

docs/ref/settings.txt

@@ -458,7 +458,7 @@ other database types. This example is for PostgreSQL::
 
     DATABASES = {
         'default': {
-            'ENGINE':'django.db.backends.postgresql_psycopg2',
+            'ENGINE': 'django.db.backends.postgresql_psycopg2',
             'NAME': 'mydatabase',
             'USER': 'mydatabaseuser',
             'PASSWORD': 'mypassword',