spark ddl with struct data type error

Describe the bug
When I execute show create table a in spark, I get the ddl sql as below:

CREATE TABLE t_a (
a bigint,
b struct <c: bigint>
)

There is a ':' that is optional between field name and field type.

Actual behavior
I input this sql in web demo.

There is a error.

An Unexpected Error Occurred
Parse error: Unexpected ": bigint> " at line 3 column 12. SQL dialect used: "spark".

Please report this at [Github issues page.](https://github.com/sql-formatter-org/sql-formatter/issues)

Stack Trace:

Error: Parse error: Unexpected ": bigint>
" at line 3 column 12.
SQL dialect used: "spark".
    at T.default.createParseError (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:235390)
    at T.default.tokenize (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:235156)
    at T.default.tokenize (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:230135)
    at T.default.tokenize (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:245337)
    at T.default.reset (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:243864)
    at T.O.feed (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:270080)
    at Object.parse (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:245475)
    at T.default.parse (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:16428)
    at T.default.format (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:16326)
    at T.formatDialect (https://unpkg.com/sql-formatter@latest/dist/sql-formatter.min.js:1:264877)

Reproduce the shown CREATE TABLE statement in the web demo using the Spark dialect and start at the Spark parser entry point indicated by the error. Trace how the struct field declaration is parsed, then verify that the reported DDL formats successfully without the unexpected colon error.