weewx-purple air doesn't work with python 3

[sjthespian]

The purple air extension needs a couple of tweaks to make it work with Python3:

> diff -ub /usr/share/weewx/user/purpleair.py.orig  /usr/share/weewx/user/purpleair.py
--- /usr/share/weewx/user/purpleair.py.orig 2020-05-28 15:01:43.429508266 -0700
+++ /usr/share/weewx/user/purpleair.py  2020-05-28 14:32:23.109570262 -0700
@@ -158,7 +158,7 @@
         self.config_dict = config_dict.get('PurpleAirMonitor', {})
         try:
             self.config_dict['hostname']
-        except KeyError, e:
+        except KeyError as e:
             raise Exception("Data will not be posted: Missing option %s" % e)

         self.config_dict.setdefault('timeout', 10) # url fetch timeout
@@ -204,7 +204,7 @@
         if self.last_ts is not None:
             try:
                 data = self.get_data(now, self.last_ts)
-            except Exception, e:
+            except Exception as e:
                 # failure to fetch data, log and then return
                 logerr(e)
                 return
@@ -259,7 +259,7 @@
     def test_collector(hostname):
         session = requests.Session()
         while True:
-            print collect_data(session, hostname, 10)
+            print(collect_data(session, hostname, 10))
             time.sleep(5)

     def test_service(hostname):

[bakerkj]

@sjthespian / @harpchad I believe this is fixed. I grabbed the pull request from @krbaker.