Minimal hack for NixOS user and other that use standalone plantuml

[AchmadFathoni]

Use plantuml package or make sure plantuml is callable in your terminal, then apply this

diff --git a/autoload/plantuml_previewer.vim b/autoload/plantuml_previewer.vim
index f48f143..712a9ff 100644
--- a/autoload/plantuml_previewer.vim
+++ b/autoload/plantuml_previewer.vim
@@ -23,10 +23,6 @@ let s:started = v:false
 let s:extensions = get(g:, "plantuml_previewer#file_pattern", "*.pu,*.uml,*.plantuml,*.puml,*.iuml")
 
 function! plantuml_previewer#start() "{{{
-  if !executable(s:java_path())
-    echoerr 'require java command'
-    return v:false
-  endif
   let viewer_path = s:viewer_path()
   if !isdirectory(viewer_path) && !filereadable(viewer_path)
     call plantuml_previewer#copy_viewer_directory()
diff --git a/script/update-viewer.sh b/script/update-viewer.sh
index 521fe05..51f71d5 100755
--- a/script/update-viewer.sh
+++ b/script/update-viewer.sh
@@ -13,6 +13,6 @@ timestamp=${8}
 update_js_path=${9}
 include_path=${10}
 
-$java -Dapple.awt.UIElement=true -Djava.awt.headless=true -Dplantuml.include.path="$include_path" -jar "$jar_path" "$puml_src_path" -t$image_type -o "$output_dir_path"
+plantuml "$puml_src_path" -t$image_type -o "$output_dir_path"
 cp "$output_path" "$finial_path"
 echo "window.updateDiagramURL('$timestamp')" > "$update_js_path"