#741: Updated reqs for leaf-bladed sword

What have you done in this MR?

• Updated leaf-bladed sword reqs to attack 50 and slayer 55 in items_config.json
• This page was used as reference: https://runescape.wiki/w/Leaf-bladed_sword?oldid=1444053

Are there any tricky things testers should keep an eye out for?

• No
• Yes, as follows:
• I have tested these changes thoroughly.
• This requires extra testing due to changes to architecture or other similarly risky changes.
• I used the Thanos Tool for any JSON edits, I did not edit any JSON files by hand (MR will be rejected if there are manual JSON edits).
• I acknowledge that this contribution will be released under the AGPL license.

I confirmed that not having attack of 50 will not let you wield. I tested having attack 50 and not having slayer 55 will not let you wield. I tested that having attack >= 50 and slayer >= 55 will let you wield.

Closes #741 (closed)