fix quota tier_key description

Signed-off-by: Narcis <narcis.davins@krakend.io>

Author: NarcisDavins

v2.13/governance/quota.json

@@ -22,7 +22,7 @@
       "type": "string"
     },
     "tier_key": {
-      "description": "Header or param used to determine the tier. Use `tier_value` and `tier_value_as` on each tier to determine how to match the value.\n\nSee: https://www.krakend.io/docs/enterprise/governance/quota/",
+      "description": "Header used to determine the tier. Use `tier_value` and `tier_value_as` on each tier to determine how to match the value.\n\nSee: https://www.krakend.io/docs/enterprise/governance/quota/",
       "examples": [ "X-User-Tier", "X-User-ID" ],
       "type": "string"
     },