all: update to go1.13.12 and go1.14.4
all: update to go1.13.12 and go1.14.4

Change-Id: I38b18cf8124fcc52d56741e0cefb68fe973ab087
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/238758
Reviewed-by: Herbie Ong <86f376bf42b6daa37c768c730acd318ab6855de4@google.com>

protocolbuffers/protobuf-go,protocolbuffers/protobuf-go