run sparsity test only with 2.5 backends

changed URL

changed URL

issue arangodb#176: bug; Invalid bind parameter value on "file" value

issue arangodb#176: bug; Invalid bind parameter value on "file" value

updated version in README

ArangoDB version 2.2.6

ArangoDB 2.2

Release v2.0.0

Release v1.4.0 (Master)