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/README.md b/lib/go/README.md
index bca4370..75d7174 100644
--- a/lib/go/README.md
+++ b/lib/go/README.md
@@ -21,6 +21,27 @@
 under the License.
 
 
+Suppored Go releases
+====================
+
+Following the
+[official Go release policy](https://golang.org/doc/devel/release#policy),
+we support the latest two Go releases at the time of the Thrift release.
+
+For example, at the time of Thrift v0.14.0 release,
+the latest two Go releases are go1.15 and go1.14,
+and those are the two Go releases supported by Thrift v0.14.*
+(including v0.14.1 and v0.14.2 patch releases).
+
+Because of Go's backward compatibility guarantee,
+older Thrift libraries usually works with newer Go releases
+(e.g. Thrift v0.14.* works with go1.16, although it's not officially supported),
+but newer Thrift releases might use new APIs introduced in Go releases and no
+longer work with older Go releases.
+For example, Thrift v0.14.0 used APIs introduced in go1.13,
+and as a result no longer works on go1.12.
+
+
 Using Thrift with Go
 ====================
 
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
+)
diff --git a/lib/go/test/fuzz/go.sum b/lib/go/test/fuzz/go.sum
new file mode 100644
index 0000000..6468215
--- /dev/null
+++ b/lib/go/test/fuzz/go.sum
@@ -0,0 +1,13 @@
+github.com/golang/mock v1.5.0/go.mod h1:CWnOUgYIOo4TcNZ0wHX3YZCqsaM1I1Jvs6v3mP3KVu8=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=