Upgrade bootstrap_form gem

- Also remove boostrap 4 migration adapter

Gemfile

@@ -128,7 +128,7 @@ gem 'asciidoctor', '~> 1.5.8'
 gem 'asciidoctor-plantuml', '0.0.8'
 gem 'rouge', '~> 3.1'
 gem 'truncato', '~> 0.7.11'
-gem 'bootstrap_form', '~> 2.7.0'
+gem 'bootstrap_form', '~> 4.2.0'
 gem 'nokogiri', '~> 1.10.1'
 gem 'escape_utils', '~> 1.1'
 

Gemfile.lock

@@ -87,7 +87,9 @@ GEM
       debug_inspector (>= 0.0.1)
     bootsnap (1.4.1)
       msgpack (~> 1.0)
-    bootstrap_form (2.7.0)
+    bootstrap_form (4.2.0)
+      actionpack (>= 5.0)
+      activemodel (>= 5.0)
     brakeman (4.2.1)
     browser (2.5.3)
     builder (3.2.3)
@@ -964,7 +966,7 @@ DEPENDENCIES
   better_errors (~> 2.5.0)
   binding_of_caller (~> 0.8.0)
   bootsnap (~> 1.4)
-  bootstrap_form (~> 2.7.0)
+  bootstrap_form (~> 4.2.0)
   brakeman (~> 4.2)
   browser (~> 2.5)
   bullet (~> 5.5.0)

app/assets/stylesheets/bootstrap_migration.scss

@@ -343,16 +343,6 @@ input[type=color].form-control {
   }
 }
 
-// Bootstrap 3 compatibility because bootstrap_form Gem is not updated yet
-.input-group-btn:first-child {
-  @extend .input-group-prepend;
-}
-
-// Bootstrap 3 compatibility because bootstrap_form Gem is not updated yet
-.input-group-btn:last-child {
-  @extend .input-group-append;
-}
-
 /*
  Bootstrap 4.1.2 introduced a new default vertical alignment which breaks our icons,
  so we need to reset the vertical alignment to the default value. See: