Update to Rails 5.1

We need to update to Rails 5.2 because of the security issue:

https://groups.google.com/forum/#!topic/rubyonrails-security/IsQKvDqZdKw

But this is not an easy update, so let's try to update in small steps.

Gemfile

@@ -10,7 +10,7 @@ if Gem::Version.new(Bundler::VERSION) < Gem::Version.new('1.8.4')
 end
 
 # as web framework
-gem 'rails', '~> 5.0.7'
+gem 'rails', '~> 5.1.0'
 
 # Use Puma as the app server
 gem 'puma', '~> 3.0'

Gemfile.lock

@@ -13,27 +13,27 @@ GEM
   remote: https://rails-assets.org/
   specs:
     Ascii85 (1.0.3)
-    actioncable (5.0.7.2)
+    actioncable (5.1.7)
-      actionpack (= 5.0.7.2)
+      actionpack (= 5.1.7)
-      nio4r (>= 1.2, < 3.0)
+      nio4r (~> 2.0)
       websocket-driver (~> 0.6.1)
-    actionmailer (5.0.7.2)
+    actionmailer (5.1.7)
-      actionpack (= 5.0.7.2)
+      actionpack (= 5.1.7)
-      actionview (= 5.0.7.2)
+      actionview (= 5.1.7)
-      activejob (= 5.0.7.2)
+      activejob (= 5.1.7)
       mail (~> 2.5, >= 2.5.4)
       rails-dom-testing (~> 2.0)
-    actionpack (5.0.7.2)
+    actionpack (5.1.7)
-      actionview (= 5.0.7.2)
+      actionview (= 5.1.7)
-      activesupport (= 5.0.7.2)
+      activesupport (= 5.1.7)
       rack (~> 2.0)
-      rack-test (~> 0.6.3)
+      rack-test (>= 0.6.3)
       rails-dom-testing (~> 2.0)
       rails-html-sanitizer (~> 1.0, >= 1.0.2)
-    actionview (5.0.7.2)
+    actionview (5.1.7)
-      activesupport (= 5.0.7.2)
+      activesupport (= 5.1.7)
       builder (~> 3.1)
-      erubis (~> 2.7.0)
+      erubi (~> 1.4)
       rails-dom-testing (~> 2.0)
       rails-html-sanitizer (~> 1.0, >= 1.0.3)
     active_model_serializers (0.10.9)
@@ -41,16 +41,16 @@ GEM
       activemodel (>= 4.1, < 6)
       case_transform (>= 0.2)
       jsonapi-renderer (>= 0.1.1.beta1, < 0.3)
-    activejob (5.0.7.2)
+    activejob (5.1.7)
-      activesupport (= 5.0.7.2)
+      activesupport (= 5.1.7)
       globalid (>= 0.3.6)
-    activemodel (5.0.7.2)
+    activemodel (5.1.7)
-      activesupport (= 5.0.7.2)
+      activesupport (= 5.1.7)
-    activerecord (5.0.7.2)
+    activerecord (5.1.7)
-      activemodel (= 5.0.7.2)
+      activemodel (= 5.1.7)
-      activesupport (= 5.0.7.2)
+      activesupport (= 5.1.7)
-      arel (~> 7.0)
+      arel (~> 8.0)
-    activesupport (5.0.7.2)
+    activesupport (5.1.7)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
       minitest (~> 5.1)
@@ -72,7 +72,7 @@ GEM
       railties (>= 4.0)
     archive-zip (0.12.0)
       io-like (~> 0.3.0)
-    arel (7.1.4)
+    arel (8.0.0)
     ast (2.4.0)
     autoprefixer-rails (9.5.1)
       execjs
@@ -168,6 +168,7 @@ GEM
     dotenv-rails (2.7.2)
       dotenv (= 2.7.2)
       railties (>= 3.2, < 6.1)
+    erubi (1.8.0)
     erubis (2.7.0)
     execjs (2.7.0)
     factory_bot (4.11.1)
@@ -381,19 +382,19 @@ GEM
     rack-openid (1.3.1)
       rack (>= 1.1.0)
       ruby-openid (>= 2.1.8)
-    rack-test (0.6.3)
+    rack-test (1.1.0)
-      rack (>= 1.0)
+      rack (>= 1.0, < 3)
-    rails (5.0.7.2)
+    rails (5.1.7)
-      actioncable (= 5.0.7.2)
+      actioncable (= 5.1.7)
-      actionmailer (= 5.0.7.2)
+      actionmailer (= 5.1.7)
-      actionpack (= 5.0.7.2)
+      actionpack (= 5.1.7)
-      actionview (= 5.0.7.2)
+      actionview (= 5.1.7)
-      activejob (= 5.0.7.2)
+      activejob (= 5.1.7)
-      activemodel (= 5.0.7.2)
+      activemodel (= 5.1.7)
-      activerecord (= 5.0.7.2)
+      activerecord (= 5.1.7)
-      activesupport (= 5.0.7.2)
+      activesupport (= 5.1.7)
       bundler (>= 1.3.0)
-      railties (= 5.0.7.2)
+      railties (= 5.1.7)
       sprockets-rails (>= 2.0.0)
     rails-assets-bootstrap (3.3.6)
       rails-assets-jquery (>= 1.9.1, < 3)
@@ -427,9 +428,9 @@ GEM
     rails-i18n (5.1.3)
       i18n (>= 0.7, < 2)
       railties (>= 5.0, < 6)
-    railties (5.0.7.2)
+    railties (5.1.7)
-      actionpack (= 5.0.7.2)
+      actionpack (= 5.1.7)
-      activesupport (= 5.0.7.2)
+      activesupport (= 5.1.7)
       method_source
       rake (>= 0.8.7)
       thor (>= 0.18.1, < 2.0)
@@ -674,7 +675,7 @@ DEPENDENCIES
   prawn-qrcode
   prawn-rails
   puma (~> 3.0)
-  rails (~> 5.0.7)
+  rails (~> 5.1.0)
   rails-assets-bootstrap-markdown!
   rails-assets-bootstrap-select!
   rails-assets-date.format!