go.mod,travis: add go 1.14.x version and drop 1.11.x version

Author: zchee

.travis.yml

@@ -1,20 +1,33 @@
 language: go
-sudo: false
+os: linux
+dist: xenial
+
+git:
+  depth: 2
+  submodules: false
+
+go:
+  - 1.12.x
+  - 1.13.x
+  - 1.14.x
+  - tip
+
+env:
+  global:
+    - CC=clang
+    - CXX=clang++
+    - GO111MODULE=on
+
+before_cache:
+  - go mod download
+
+cache:
+  directories:
+    - $GOPATH/pkg/mod
 
 before_install:
   - eval "$(curl -Ss https://raw.githubusercontent.com/neovim/bot-ci/master/scripts/travis-setup.sh) nightly-x64"
 
-matrix:
-  include:
-  - go: 1.11.x
-    env: GO111MODULE=on
-  - go: 1.12.x
-    env: GO111MODULE=on
-  - go: 1.13.x
-    env: GO111MODULE=on
-  - go: tip
-    env: GO111MODULE=on
-
 script:
   - go get -t -v ./...
   - diff -u <(echo -n) <(gofmt -d .)

go.mod

@@ -1,3 +1,3 @@
 module github.com/neovim/go-client
 
-go 1.11
+go 1.12