patch 9.0.1807: runtime: crystal scripts not recognised

Problem:  runtime: crystal scripts not recognised
Solution: Filetype detect Crystal scripts by shebang line

closes: #12935

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Doug Kearns <dougkearns@gmail.com>
diff --git a/runtime/autoload/dist/script.vim b/runtime/autoload/dist/script.vim
index 5f3ae4a..6163003 100644
--- a/runtime/autoload/dist/script.vim
+++ b/runtime/autoload/dist/script.vim
@@ -209,6 +209,10 @@
   elseif name =~ 'nix-shell'
     return 'nix'
 
+    # Crystal
+  elseif name =~ '^crystal\>'
+    return 'crystal'
+
   endif
 
   return ''