Allow folding of docstrings

Author: Iuri Fernandes

syntax/elixir.vim

@@ -59,8 +59,8 @@ syn cluster elixirStringContained contains=elixirInterpolation,elixirRegexEscape
 syn region elixirString matchgroup=elixirDelimiter start="'" end="'" skip="\\'"
 syn region elixirString matchgroup=elixirDelimiter start='"' end='"' skip='\\"' contains=@elixirStringContained
 syn region elixirInterpolation matchgroup=elixirDelimiter start="#{" end="}" contained contains=ALLBUT,elixirComment,@elixirNotTop
-syn region elixirDocString start=+"""+ end=+"""+ contains=elixirTodo
-syn region elixirDocString start=+'''+ end=+'''+ contains=elixirTodo
+syn region elixirDocString start=+"""+ end=+"""+ contains=elixirTodo fold
+syn region elixirDocString start=+'''+ end=+'''+ contains=elixirTodo fold
 
 syn match elixirSymbolInterpolated ':\("\)\@=' contains=elixirString
 syn match elixirString "\(\w\)\@<!?\%(\\\(x\d{1,2}\|\h{1,2}\h\@!\>\|0[0-7]{0,2}[0-7]\@!\>\|[^x0MC]\)\|(\\[MC]-)+\w\|[^\s\\]\)"