Handle version exclusion constraint

Handle gem version exclusion from gemspec ( != symbol )

/reviewed-by @kirr
/reviewed-on !6
6 jobs for master in 0 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:10:44

passed SlapOS.Eggs.UnitTest-Master.Python3

00:08:40

passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:57

passed SlapOS.Eggs.UnitTest-Master.Python2

00:24:15

passed SlapOS.Eggs.UnitTest-Master.Python3

00:13:04

passed SlapOS.Eggs.UnitTest-Master.Python3

00:09:50