The following liquibase changeset does not work as expected

```xml
        <createTable tableName="test">
            <column name="id" type="SERIAL">
                <constraints nullable="false" primaryKey="true"/>
            </column>
        </createTable>
```

This changeset results in sql

```sql
CREATE TABLE test (id INTEGER NOT NULL, CONSTRAINT TEST_PKEY PRIMARY KEY (id));
```

In liquibase 3.6.3 and earlier the type `SERIAL` was used for the column which means that a sequence is automatically included.

This issue seems to be caused by #874
It appears that SERIAL columns are replaced by INT, however liquibase does reconize that this column type is an auto increment column.

It would be acceptible if the generated sql would be

```sql
CREATE TABLE test (id INTEGER GENERATED BY DEFAULT AS IDENTITY NOT NULL, CONSTRAINT TEST_PKEY PRIMARY KEY (id));
```


public String toString() {
        String returnString = getName();
        if ((parameters != null) && !parameters.isEmpty() && (maxParameters > 0)) {
            returnString += "(";
            for (Object param : parameters) {
                if (returnString == null) {
                    returnString += "NULL,";
                }
                returnString += param.toString()+",";
            }
            returnString = returnString.replaceFirst(",$", "");
            returnString += ")";
        }
        if (additionalInformation != null) {
            returnString += " "+additionalInformation;
        }
        return returnString.trim();
    }
    @Override
    public boolean equals(final Object o) {
        return (o instanceof LiquibaseDataType) && toString().equals(o.toString());
    }
    @Override
    public int hashCode() {
        return toString().hashCode();
    }
    /**
     * Determines if the given function name refers to the function that returns the current
     * time and date for a specific DBMS. Also returns true if the name returns the Liquibase wildcard
     * CURRENT_DATE_TIME_PLACE_HOLDER, which will later be translated into the appropriate function.