storage: gcc8: standardize use of std::filesystem

This was already done repo-wide with 185b9f8b but this one spot appears
to have been missed, and was caught by gcc8:

| ../git/storagehandler.cpp:276:39: error: 'filesystem' is not a namespace-name
|      namespace fs = std::experimental::filesystem;
|                                        ^~~~~~~~~~

Change-Id: I79d70f0ba1268eae9fc76be690313a5128b59f17
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
1 file changed