test add: change column with COMMENT then COMMENT not included
test add: change column with COMMENT then COMMENT not included

```
$ go test -v ./diff

=== RUN   TestDiff
--- FAIL: TestDiff (0.00s)
        Error Trace:    diff_test.go:94
        Error:          Not equal:
                        expected: "ALTER TABLE `fuga` CHANGE COLUMN `id` `id` INTEGER NOT NULL COMMENT 'fuga is good';"
                        received: "ALTER TABLE `fuga` CHANGE COLUMN `id` `id` INTEGER NOT NULL 'fuga is good';"
        Messages:       result SQL should match
FAIL
exit status 1
FAIL    github.com/schemalex/schemalex/diff     0.018s
```

schemalex/schemalex,soh335/schemalex,schemalex/schemalex