Redis v6 (current stable) is not compatible with CentOS 7

[jenkin]

Problem: row 29 fails building redis-cli (stable version)

Cause: row 13 in CentOS 7 installs gcc v4.8.5 but gcc >= 4.9 is required to build redis v6 (current stable version)

Solution: stick to redis v5.0.9 (last version of v5 branch)