Allow up to 5.1 versioned migrations

manageiq isn't yet on rails 5.2 so it can't process 5.2 versioned
migrations as seen at least once already, such as ManageIQ#379.

ManageIQ/manageiq#18076 is adding rails 5.1
support to manageiq, so let's change schema to 5.1 for now while we work
on 5.2 for manageiq.

manageiq-schema.gemspec

@@ -21,7 +21,7 @@ Gem::Specification.new do |s|
   s.add_dependency "more_core_extensions", "~> 3.5"
   s.add_dependency "pg"
   s.add_dependency "pg-pglogical", "~> 2.1.1"
-  s.add_dependency "rails", ">= 5.0.7.1", "!= 5.2.0.x", "!= 5.2.1.0", "< 5.3"
+  s.add_dependency "rails", ">= 5.0.7.1", "< 5.2"
 
   s.add_development_dependency "codeclimate-test-reporter", "~> 1.0.0"
   s.add_development_dependency "rspec"