Add license type: MIT is a NOTICE license

Bug: 68860345
Bug: 69058154
Bug: 151953481

Test: no code changes
Change-Id: I88b00bbdc96082a86aca379349bb6f36e3dc0db5
diff --git a/METADATA b/METADATA
index 67e629f..59680f8 100644
--- a/METADATA
+++ b/METADATA
@@ -8,5 +8,6 @@
     value: "https://github.com/KhronosGroup/SPIRV-Headers.git"
   }
   version: "d5b2e1255f706ce1f88812217e9a554f299848af"
+  license_type: NOTICE
   last_upgrade_date { year: 2018 month: 12 day: 17 }
 }