Fix aspect ratio calculation

Gemfile.lock

+PATH
+  remote: .
+  specs:
+    jekyll-img-srcset (0.1.0)
+      jekyll (~> 4.0)
+      mini_magick
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    addressable (2.7.0)
+      public_suffix (>= 2.0.2, < 5.0)
+    colorator (1.1.0)
+    concurrent-ruby (1.1.5)
+    em-websocket (0.5.1)
+      eventmachine (>= 0.12.9)
+      http_parser.rb (~> 0.6.0)
+    eventmachine (1.2.7)
+    ffi (1.11.3)
+    forwardable-extended (2.6.0)
+    http_parser.rb (0.6.0)
+    i18n (1.7.0)
+      concurrent-ruby (~> 1.0)
+    jekyll (4.0.0)
+      addressable (~> 2.4)
+      colorator (~> 1.0)
+      em-websocket (~> 0.5)
+      i18n (>= 0.9.5, < 2)
+      jekyll-sass-converter (~> 2.0)
+      jekyll-watch (~> 2.0)
+      kramdown (~> 2.1)
+      kramdown-parser-gfm (~> 1.0)
+      liquid (~> 4.0)
+      mercenary (~> 0.3.3)
+      pathutil (~> 0.9)
+      rouge (~> 3.0)
+      safe_yaml (~> 1.0)
+      terminal-table (~> 1.8)
+    jekyll-sass-converter (2.0.1)
+      sassc (> 2.0.1, < 3.0)
+    jekyll-watch (2.2.1)
+      listen (~> 3.0)
+    kramdown (2.1.0)
+    kramdown-parser-gfm (1.1.0)
+      kramdown (~> 2.0)
+    liquid (4.0.3)
+    listen (3.2.0)
+      rb-fsevent (~> 0.10, >= 0.10.3)
+      rb-inotify (~> 0.9, >= 0.9.10)
+    mercenary (0.3.6)
+    mini_magick (4.9.5)
+    pathutil (0.16.2)
+      forwardable-extended (~> 2.6)
+    public_suffix (4.0.1)
+    rake (12.3.3)
+    rb-fsevent (0.10.3)
+    rb-inotify (0.10.0)
+      ffi (~> 1.0)
+    rouge (3.13.0)
+    safe_yaml (1.0.5)
+    sassc (2.2.1)
+      ffi (~> 1.9)
+    terminal-table (1.8.0)
+      unicode-display_width (~> 1.1, >= 1.1.1)
+    unicode-display_width (1.6.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  bundler (~> 1.16)
+  jekyll-img-srcset!
+  rake (~> 12.0)
+
+BUNDLED WITH
+   1.17.2

lib/jekyll-img-srcset.rb

@@ -3,7 +3,7 @@ require 'mini_magick'
 def resize_image(url, widths, dest, base_image_path)
     image = MiniMagick::Image.open(File.join(base_image_path, url))
     w = image.dimensions[0]
-    aspect = image.dimensions[1] / w
+    aspect = image.dimensions[1].to_f / w
     new_widths = widths.select {|x| x <= w}
     new_widths.map do |width| 
         [width, File.join(dest, base_image_path, "#{width}", url)]