SI-6773 Changes IndexSeqFactory to be "since 2.11"

The addition of IndexSeqFactory to 2.10.x branch created a binary
incompatibility so it was removed in that branch before being released.
This commit fixes the since annotation to 2.11 on IndexSeqFactory in the
master branch.
Merge pull request #2071 from JamesIry/master_SI-6773

SI-6773 Changes IndexSeqFactory to be "since 2.11"