Correct test hash in write test

A previous change in the merge of branch feature/gas_objects
(sha: 8a8e607d717f731c573e6c4adddd355411284558) failed to account for the
internal changes to the mesh structure that led to functionally equivalent but
different file. Thus this fixes the hash.
Merge pull request #5 from aepsil0n/fix/test_hash

Correct test hash in write test