update magic rope spell

fixes this error:

Lua Script Error: [Spell Interface]
data/spells/scripts/support/magic rope.lua:onCastSpell
attempt to index a number value
stack traceback:
[C]: at 0x0015dbd0
[C]: in function 'getThingfromPos'
data/spells/scripts/support/magic rope.lua:4: in function cripts/support/magic rope.lua:1>