THRIFT-5447: Update supported Go versions

Client: go

Update go versions used in travis to 1.16.7 and 1.17, update
LANGUAGES.md, and update go's README to clarify on support policy.

This change will be cherry-picked into 0.15.0 branch after merged.
diff --git a/lib/go/test/fuzz/go.mod b/lib/go/test/fuzz/go.mod
index efff516..3cefa02 100644
--- a/lib/go/test/fuzz/go.mod
+++ b/lib/go/test/fuzz/go.mod
@@ -1,9 +1,15 @@
 module github.com/apache/thrift/lib/go/test/fuzz
 
-go 1.15
+go 1.16
 
 replace github.com/apache/thrift => ../../../../
 
 replace shared => ./gen-go/shared
 
 replace tutorial => ./gen-go/tutorial
+
+require (
+	github.com/apache/thrift v0.0.0-00010101000000-000000000000
+	shared v0.0.0-00010101000000-000000000000
+	tutorial v0.0.0-00010101000000-000000000000
+)