fix for image.path causing an invalid url error

lib/jekyll-seo-tag/drop.rb

@@ -168,7 +168,8 @@ module Jekyll
         image["path"] ||= image["facebook"] || image["twitter"]
         return @image = nil unless image["path"]
 
-        unless absolute_url? image["path"]
+        # absolute_url? will return nil for an invalid URL
+        if absolute_url?(image["path"]) == false
           image["path"] = filters.absolute_url image["path"]
         end
 

spec/jekyll_seo_tag/drop_spec.rb

@@ -563,7 +563,7 @@ RSpec.describe Jekyll::SeoTag::Drop do
         let(:image) { ":" }
 
         it "returns nil" do
-          expect(subject.image["path"]).to eql("/:")
+          expect(subject.image["path"]).to eql(":")
         end
       end