message: docs: change gcc demand to 4.8
diff: -*We have tested on linux server with CentOS 6.2 x86_64 and CentOS 6.6 x86_64. The version of GCC should be 4.4.7 or later.*
  +*We have tested on linux server with CentOS 6.2 x86_64 and CentOS 6.6 x86_64. The version of GCC should be 4.8 or later.*
  Item | Requirement
  :-- | :--
  