only use 'j' format option if available

Fixes #13 and #15, part of #14

ftplugin/fish.vim

@@ -2,12 +2,17 @@ setlocal comments=:#
 setlocal commentstring=#%s
 setlocal define=\\v^\\s*function>
 setlocal foldexpr=fish#Fold()
-setlocal formatoptions+=ron1j
+setlocal formatoptions+=ron1
 setlocal formatoptions-=t
 setlocal include=\\v^\\s*\\.>
 setlocal iskeyword=@,48-57,-,_,.,/
 setlocal suffixesadd^=.fish
 
+" Use the 'j' format option when available.
+if v:version ># 703 || v:version ==# 703 && has('patch541')
+    setlocal formatoptions+=j
+endif
+
 if executable('fish_indent')
     setlocal formatexpr=fish#Format()
 endif