cave/trend_tag: ignore spammy tags

cave/src/trend_tag.rs

@@ -83,6 +83,11 @@ impl TrendTag {
     }
 
     pub fn score(&self, period: u64, until: u64) -> f64 {
+        // ignore spam that comes from only 1 instance
+        if self.hosts().skip(1).next().is_none() {
+            return -1000.;
+        }
+
         let from = until - period;
         let mut before_mentions = 0;
         let mut before_hours = 0;