check for underscore for https

lib/github-pages-health-check/domain.rb

@@ -449,8 +449,11 @@ def enforces_https?
       def https_eligible?
         # Can't have any IP's which aren't GitHub's present.
         return false if non_github_pages_ip_present?
-        # Must be a CNAME or point to our IPs.
 
+        # Can't have underscores in the domain name (Let's Encrypt does not allow it)
+        return false if host.include?("_")
+
+        # Must be a CNAME or point to our IPs.
         # Only check the one domain if a CNAME. Don't check the parent domain.
         return true if cname_to_github_user_domain?
 

lib/github-pages-health-check/version.rb

@@ -2,6 +2,6 @@
 
 module GitHubPages
   module HealthCheck
-    VERSION = "1.18.0"
+    VERSION = "1.18.1"
   end
 end

spec/github_pages_health_check/domain_spec.rb

@@ -1042,6 +1042,12 @@
 
       it { is_expected.to be_https_eligible }
 
+      context "with underscore domain" do
+        let(:domain) { "foo_bar.com" }
+
+        it { is_expected.not_to be_https_eligible }
+      end
+
       context "with bad CAA records" do
         let(:caa_domain) { "digicert.com" }
         before(:each) { allow(subject.send(:caa)).to receive(:query) { [caa_packet] } }