update import thrift/lib/thrift/metadata to github.com/facebook/fbthr…

…ift/thrift/lib/thrift/metadata

Summary:
In preparation of D62942743 we are renaming `thrift/lib/thrift/metadata` to `github.com/facebook/fbthrift/thrift/lib/thrift/metadata`
More details and reasons for this change in the description of D62942743

Reviewed By: echistyakov

Differential Revision: D62946237

fbshipit-source-id: 6dc04782def3f8c716e3c3827b6f6563213a6ee0

third-party/thrift/src/thrift/lib/thrift/metadata.thrift

@@ -21,7 +21,7 @@ namespace py.asyncio apache_thrift_asyncio.metadata
 namespace py3 apache.thrift
 namespace js apache.thrift
 namespace php tmeta
-namespace go thrift.lib.thrift.metadata
+namespace go 'github.com/facebook/fbthrift/thrift/lib/thrift/metadata'
 
 /*
  * 'metadata.thrift' is currently frozen in favor of 'schema.thrift'.