Change PRERELEASE for branch

MSP-10637
Generalize groups for operators and operations

MSP-10637

Extract the general behavior of Operator::Union to
Operator::Group::Base.  Then have Operator::Group::Union and
Operator::Group::Base as subclasses so that visit can be tuned based the
class being a union or intersection.  Do the same changes for
Operations.  Operator and Operation level intersection are needed so
that an intersection can be forced when the operator is the same as the
normal query.tree lock does a group_by(:operator) that unions operations
with the same operator.
Fix yard undocumented objects

MSP-10637

YARD 0.8.7.4 has a bug where docs for @!attribute aren't attached to the
attribute writer.
Bump version for prerelease gem

MSP-10637

MINOR version is incremented because the classes were renamed to add the
Group namespace.
Fix version_spec.rb for tags

MSP-10637

Tag names for `rake release` use the `.pre.` join in the .gem version
name instead of the `-` in `VERSION`, so the spec needs to be updated to
parse the `.pre.` format back into the `-` VERSION format when
comparing.
Bump version

MSP-10637

Bump minor version for version_spec.rb fix so that a new tag can be
created to test that the tag build is fixed on travis-ci.
Merge pull request #17 from rapid7/feature/MSP-10637/metasploit-model-search-operator-and-operation-groups

Metasploit::Model::Search::Operator and Operation Groups

MSP-10637 #land