rename attribute env-idea to kroki-force-png as this attribute name i…

…s leaking an implementation details from an early version of this plugin

ruby/lib/asciidoctor/extensions/asciidoctor_kroki/extension.rb

@@ -146,8 +146,8 @@ def get_role(format, role)
 
       def get_format(doc, attrs, diagram_type)
         format = attrs['format'] || 'svg'
-        # The JavaFX preview doesn't support SVG well, therefore we'll use PNG format...
-        if doc.attr?('env-idea') && format == 'svg'
+        # If the media we're preparing for doesn't support SVG well, use PNG instead...
+        if doc.attr?('kroki-force-png') && format == 'svg'
           # ... unless the diagram library does not support PNG as output format!
           # Currently, mermaid, nomnoml, svgbob, wavedrom only support SVG as output format.
           svg_only_diagram_types = %w[:mermaid :nomnoml :svgbob :wavedrom]

ruby/spec/asciidoctor_kroki_spec.rb

@@ -20,14 +20,14 @@
 </div>
 </div>)
     end
-    it 'should use png if env-idea is defined' do
+    it 'should use png if kroki-force-png is defined' do
       input = <<~'ADOC'
         [plantuml]
         ....
         alice -> bob: hello
         ....
       ADOC
-      output = Asciidoctor.convert(input, attributes: { 'env-idea' => '' }, standalone: false)
+      output = Asciidoctor.convert(input, attributes: { 'kroki-force-png' => '' }, standalone: false)
       (expect output).to eql %(<div class="imageblock kroki">
 <div class="content">
 <img src="https://kroki.io/plantuml/png/eNpLzMlMTlXQtVNIyk-yUshIzcnJBwA9iwZL" alt="Diagram">
@@ -41,7 +41,7 @@
         alice -> bob: hello
         ....
       ADOC
-      output = Asciidoctor.convert(input, attributes: { 'env-idea' => '', 'kroki-plantuml-include' => 'spec/fixtures/config.puml' }, standalone: false)
+      output = Asciidoctor.convert(input, attributes: { 'kroki-force-png' => '', 'kroki-plantuml-include' => 'spec/fixtures/config.puml' }, standalone: false)
       (expect output).to eql %(<div class="imageblock kroki">
 <div class="content">
 <img src="https://kroki.io/plantuml/png/eNorzs7MK0gsSsxVyM3Py0_OKMrPTVUoKSpN5eJKzMlMTlXQtVNIyk-yUshIzcnJBwCT9xBc" alt="Diagram">