Added missing µ in tweet msg

tweet.py

@@ -90,7 +90,7 @@ def may_tweet_again():
 if pm_10_0 is not None and pm_2_50 is not None and float(pm_10_0) > conf_limit_pm_10_0:
     current_time = strftime("%Y-%m-%d %H:%M:%S UTC", gmtime())
 
-    message = "{} #{}\n⚠ PM10: {}g/m³, PM2.5: {}µg/m³, {}°C, RH:{}%\nDetails: {}\nThis is a bot, code available on github aschuma/air_tweets\n".format(
+    message = "{} #{}\n⚠ PM10: {}µg/m³, PM2.5: {}µg/m³, {}°C, RH:{}%\nDetails: {}\nThis is a bot, code available on github aschuma/air_tweets\n".format(
         conf_twitter_msg_preamble,
         conf_twitter_tag_bot,
         pm_10_0,