Correct the transaction hook location in the example spring-txn

The glue path in ```@CucumberOption``` annotation of the RunCukesTest in the spring transaction example, was not updated when the SpringTransactionHook class was moved from cucumber.runtime.java.spring.hooks to cucumber.api.spring. Therefore the example is currently actually a "spring-without-transactions-example".

This change cannot be merged until #637 has been resolved.