Upon tagging a repository, an error due to a missing migration occurred:
```
PG::Error: ERROR: column "taggings_count" does not exist
LINE 1: UPDATE "tags" SET "taggings_count" = COALESCE("taggings_coun...
```
Ran `rake acts_as_taggable_on_engine:install:migrations`, removed the first
migration that created the `tags` and `taggings` table, and added the rest.
Closes#1512
Closes https://github.com/gitlabhq/gitlabhq/issues/6867
Closes https://github.com/gitlabhq/gitlabhq/issues/9194
Stan Hu