THRIFT-5338: Raise minimal supported go version to 1.14.14

Client: go

- Update Dockerfiles used by travis
- Add go.mod file
- Modify error handling code to take advantage of errors package updates
  in go1.13
diff --git a/build/docker/ubuntu-xenial/Dockerfile b/build/docker/ubuntu-xenial/Dockerfile
index 535db41..e554c53 100644
--- a/build/docker/ubuntu-xenial/Dockerfile
+++ b/build/docker/ubuntu-xenial/Dockerfile
@@ -137,9 +137,9 @@
       libglib2.0-dev
 
 # golang
-ENV GOLANG_VERSION 1.10.8
+ENV GOLANG_VERSION 1.14.14
 ENV GOLANG_DOWNLOAD_URL https://golang.org/dl/go$GOLANG_VERSION.linux-amd64.tar.gz
-ENV GOLANG_DOWNLOAD_SHA256 d8626fb6f9a3ab397d88c483b576be41fa81eefcec2fd18562c87626dbb3c39e
+ENV GOLANG_DOWNLOAD_SHA256 6f1354c9040d65d1622b451f43c324c1e5197aa9242d00c5a117d0e2625f3e0d
 RUN curl -fsSL "$GOLANG_DOWNLOAD_URL" -o golang.tar.gz && \
       echo "$GOLANG_DOWNLOAD_SHA256  golang.tar.gz" | sha256sum -c - && \
       tar -C /usr/local -xzf golang.tar.gz && \