Fix test relations paths

[thisisaaronland]

Test relations are stored as bz2-encoded files but the reader doesn't check for {URI}.bz2

> go test -v ./...
=== RUN   TestIndexFeatures
2022/05/06 15:42:17 Failed to read '102/191/575/102191575.geojson' because 'Failed to stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/102/191/575/102191575.geojson, stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/102/191/575/102191575.geojson: no such file or directory'. Strict mode is disabled so skipping
2022/05/06 15:42:17 Failed to read '856/330/41/85633041.geojson' because 'Failed to stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/856/330/41/85633041.geojson, stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/856/330/41/85633041.geojson: no such file or directory'. Strict mode is disabled so skipping
2022/05/06 15:42:17 Failed to read '136/251/273/136251273.geojson' because 'Failed to stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/136/251/273/136251273.geojson, stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/136/251/273/136251273.geojson: no such file or directory'. Strict mode is disabled so skipping
2022/05/06 15:42:17 Failed to read '890/458/661/890458661.geojson' because 'Failed to stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/890/458/661/890458661.geojson, stat /usr/local/whosonfirst/go-whosonfirst-sqlite-features-index/fixtures/relations/890/458/661/890458661.geojson: no such file or directory'. Strict mode is disabled so skipping
2022/05/06 15:42:17 time to index paths (1) 21.594868ms
--- PASS: TestIndexFeatures (0.02s)