fish: functions/b: Take number of levels to go back up the directory

fish/.config/fish/functions/b.fish

@@ -1,3 +1,10 @@
-function b --wraps='cd ..' --description 'alias b=cd ..'
-  cd .. $argv; 
+function b --description 'Move up the directory specified number of times'
+  if test -z $argv[1]
+    set n 1
+  else
+    set n $argv[1]
+  end
+  for i in (seq $n)
+    cd ..
+  end
 end