bsip18: update status -> installed

Author: abitmore

bsip-0018.md

@@ -1,7 +1,7 @@
-    BSIP: 00018
+    BSIP: 0018
     Title: Revive BitAsset through buying Settlement Pool
     Authors: Fabian Schuh, Peter Conrad
-    Status: Implemented
+    Status: Installed
     Type: Protocol
     Created: 2017-06-05
     Discussion: https://bitsharestalk.org/index.php/topic,24322.0.html