Update version guard

fix up 98ef38ada43338c073f50a0093196f0356284625

spec/ruby/core/regexp/initialize_spec.rb

@@ -5,13 +5,13 @@ describe "Regexp#initialize" do
     Regexp.should have_private_method(:initialize)
   end
 
-  ruby_version_is ""..."2.7" do
+  ruby_version_is ""..."2.8" do
     it "raises a SecurityError on a Regexp literal" do
       -> { //.send(:initialize, "") }.should raise_error(SecurityError)
     end
   end
 
-  ruby_version_is "2.7" do
+  ruby_version_is "2.8" do
     it "raises a FrozenError on a Regexp literal" do
       -> { //.send(:initialize, "") }.should raise_error(FrozenError)
     end

spec/ruby/language/regexp_spec.rb

@@ -18,7 +18,7 @@ describe "Literal Regexps" do
     /Hello/.should be_kind_of(Regexp)
   end
 
-  ruby_version_is "2.7" do
+  ruby_version_is "2.8" do
     it "is frozen" do
       /Hello/.frozen?.should == true
     end