bak: fixed directory handling

plugins/bak/bak.load

 function __bak_name
   # trim / for directories
-  set arg (echo $argv[1] | sed "s/\///")
+  set arg (echo $argv[1] | sed 's/\/$//')
   echo "$arg.(date +"%Y%m%d_%H%M%S").bak"
 end
 

plugins/bak/cpbak.fish

@@ -2,5 +2,5 @@
 # (c) Roman Inflianskas (rominf) <infroma@gmail.com>, 2014
 
 function cpbak
-  __bak cp $argv
+  __bak 'cp -a' $argv
 end