Updated to allow Ruby 3.1

Gemfile

@@ -3,9 +3,9 @@ source 'https://rubygems.org'
 gem 'thin'
 gem 'sinatra'
 gem 'sinatra-contrib'
-gem 'prawn', '2.2.2'
+gem 'prawn'
-gem 'prawn-templates', '0.1.1'
+gem 'prawn-templates'
 
 group :development do
   gem 'rerun'
-end
+end

Gemfile.lock

@@ -1,71 +1,69 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    Ascii85 (1.0.3)
+    Ascii85 (1.1.0)
     afm (0.2.2)
-    backports (3.15.0)
+    daemons (1.4.1)
-    daemons (1.3.1)
     eventmachine (1.2.7)
-    ffi (1.11.1)
+    ffi (1.15.5)
     hashery (2.1.2)
-    listen (3.1.5)
+    listen (3.8.0)
-      rb-fsevent (~> 0.9, >= 0.9.4)
+      rb-fsevent (~> 0.10, >= 0.10.3)
-      rb-inotify (~> 0.9, >= 0.9.7)
+      rb-inotify (~> 0.9, >= 0.9.10)
-      ruby_dep (~> 1.2)
+    multi_json (1.15.0)
-    multi_json (1.13.1)
+    mustermann (3.0.0)
-    mustermann (1.0.3)
+      ruby2_keywords (~> 0.0.1)
-    pdf-core (0.7.0)
+    pdf-core (0.9.0)
-    pdf-reader (2.2.0)
+    pdf-reader (2.11.0)
-      Ascii85 (~> 1.0.0)
+      Ascii85 (~> 1.0)
       afm (~> 0.2.1)
       hashery (~> 2.0)
       ruby-rc4
       ttfunk
-    prawn (2.2.2)
+    prawn (2.4.0)
-      pdf-core (~> 0.7.0)
+      pdf-core (~> 0.9.0)
-      ttfunk (~> 1.5)
+      ttfunk (~> 1.7)
-    prawn-templates (0.1.1)
+    prawn-templates (0.1.2)
       pdf-reader (~> 2.0)
       prawn (~> 2.2)
-    rack (2.0.7)
+    rack (2.2.8)
-    rack-protection (2.0.5)
+    rack-protection (3.1.0)
-      rack
+      rack (~> 2.2, >= 2.2.4)
-    rb-fsevent (0.10.3)
+    rb-fsevent (0.11.2)
-    rb-inotify (0.10.0)
+    rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rerun (0.13.0)
+    rerun (0.14.0)
       listen (~> 3.0)
     ruby-rc4 (0.1.5)
-    ruby_dep (1.5.0)
+    ruby2_keywords (0.0.5)
-    sinatra (2.0.5)
+    sinatra (3.1.0)
-      mustermann (~> 1.0)
+      mustermann (~> 3.0)
-      rack (~> 2.0)
+      rack (~> 2.2, >= 2.2.4)
-      rack-protection (= 2.0.5)
+      rack-protection (= 3.1.0)
       tilt (~> 2.0)
-    sinatra-contrib (2.0.5)
+    sinatra-contrib (3.1.0)
-      backports (>= 2.8.2)
       multi_json
-      mustermann (~> 1.0)
+      mustermann (~> 3.0)
-      rack-protection (= 2.0.5)
+      rack-protection (= 3.1.0)
-      sinatra (= 2.0.5)
+      sinatra (= 3.1.0)
-      tilt (>= 1.3, < 3)
+      tilt (~> 2.0)
-    thin (1.7.2)
+    thin (1.8.2)
       daemons (~> 1.0, >= 1.0.9)
       eventmachine (~> 1.0, >= 1.0.4)
       rack (>= 1, < 3)
-    tilt (2.0.9)
+    tilt (2.2.0)
-    ttfunk (1.5.1)
+    ttfunk (1.7.0)
 
 PLATFORMS
-  ruby
+  x86_64-linux
 
 DEPENDENCIES
-  prawn (= 2.2.2)
+  prawn
-  prawn-templates (= 0.1.1)
+  prawn-templates
   rerun
   sinatra
   sinatra-contrib
   thin
 
 BUNDLED WITH
-   1.17.2
+   2.3.7