Set filetype based on node shebang

Recognizes the node shebang line and sets the filetype to javascript.
Syntax highlights the shebang as well.

ftdetect/javascript.vim

@@ -0,0 +1,6 @@
+function! s:DetectJS()
+    if getline(1) =~# '^#!.*/bin/env\s\+node\>'
+        setfiletype javascript
+    endif
+endfunction
+autocmd BufNewFile,BufRead * call s:DetectJS()