replaced broken migration (#4) with correct version

migrations.moon

@@ -27,7 +27,7 @@ import Tracks, Tags from require "models"
     }
       add_column "tracks", unpack column
   [3]: =>
-    -- NOTE: bad migration!
+    -- NOTE: bad migration! (introduces more tags than it should)
     for track in *Tracks\select "*"
       tags = ""
       for field in *{"artist", "mood", "link", "genre"}
@@ -37,7 +37,7 @@ import Tracks, Tags from require "models"
         track.tags = process_tags trim(track.tags or "untagged") .. tags
         track\update "tags"
   [4]: =>
-    -- WARNING: removes all tags!
+    -- NOTE: bad migration! (doesn't save changes to database)
     for track in *Tracks\select "*"
       tags = ""
       for field in *{"artist", "mood", "link", "genre"}
@@ -62,5 +62,16 @@ import Tracks, Tags from require "models"
           tags[name] = 1
     for name, count in pairs tags
       Tags\create { :name, :count }
-
+  [6]: =>
+    -- WARNING: removes all tags!
+    for track in *Tracks\select "*"
+      tags = ""
+      for field in *{"artist", "mood", "link", "genre"}
+        if track[field] and #track[field] > 0
+          tags ..= " #{field}:#{track[field]}"
+      if #tags > 0
+        track.tags = process_tags "untagged" .. tags
+      else
+        track.tags = " untagged "
+      track\update "tags"
 }